I have Platinum and I only use the included plug-ins.  It is a hobby for me and I probably don't produce "pro" sounding stuff (but that is more likely due to talent, creativity and experience) than the tools.
 
The instruments are good and the FX are good (especially the Pro Channel).  Sure, you can spend more money and get better, but its more money than you'd spend on the upgrade to Platinum.
 
Again, lifetime updates are the icing on the proverbial cake.

Arizona
Based on much of the advice given so far, I understand that the lifetime upgrades are the main advantage for Platinum. I was hoping someone would mention other *particular* features, but I guess the additional features are not very compelling. I guess it's better to buy third-party plugins instead. 

I owned Producer addition and made the switch to Platinum when the lifetime updates were offered. Like it or not, lifetime updates ARE a feature. And for me, that feature, and its impact on my wallet over time were more than compelling enough. 

That being said, here's what I have found useful since switching. The additional pro channel plugs are very useful. I use the 1176 and the EQ on just about every new project. The additional add packs for Addictive Drums are also something that I will actually use and likely would have bought anyway. Those two items alone are probably worth 90% of the cost of the upgrade for me. When you add the lifetime updates on top of that, it became stupid for me not to upgrade.

The bundled synths? I have never done more than just noodle with them. I can't say I'll never use them in a project because you never know. But I can say that none of them will ever be my goto instrument for anything.

But yeah the free lifetime updates alone make it a no-brainer. You could just own Producer and never update it and that works. I'm assuming since you're still using a version of Windows that is no longer supported in any kind of fashion, you're someone who chooses to not update at all ever. And that's fine and like I said, it works. Whatever works about your software will keep working and whatever is wonky will keep being wonky and if you can live with that, great.


But here's the thing. With Sonar, the updates are not just for fixing bugs. New features are added all the time. If you don't care about getting new features, then maybe Platinum isn't for you. I made the switch and I don't regret spending the money. I don't know of anyone who has made the switch that regrets spending the money. But I also don't know every person who made the switch.

Arizona, as to instruments...you get the full version of Rapture (not the newer Rapture Pro that also loads Dimension Pro files, the original one) with Platinum. This has been one of my absolute favorite instruments ever since it first appeared. I can't think of any track I've done over the past several years that doesn't use it somewhere, and several tracks have four or five instances. It was the first synth I found that could do extensive modulation, which made it perfect for EDM but it could also do straight ahead synth sounds - I posted a comparison online once of Arturia's Minimoog V playing the same thing as Rapture with big filter sweeps etc...no one could tell the difference.
 
You also get Dimension Pro which has a large library, and Rapture Session. To me the presets/samples are hit-and-miss. Some are useless, some have become go-to presets. Admittedly the fact that I use mostly my own samples and presets factors into that opinion.
 

Tonight, I was reminded of one more thing about Cakewalk plug-ins: no iLok :)

Yes, the number one feature that makes PLATINUM worth buying is the current offer of lifetime updates.  This alone is worth the money.  I may go 2 or 3 years without updating the core software, but at least the option is there.
 
I still run win 7 pro.  I have an M-audio ProFire 2626 (firewire).  When I went to update to Windows 10, I got a rude awakening.  M-audio is not going to update the driver for the profire 2626.  The unit is good and functional, I rolled back to win 7 pro for that 1 piece of equipment. 
 
I bought a laptop with Windows 10 ugh.... Went to put Sonar X3 on it... it did NOT play nice.  Sometimes the hardware that you have and works great with what you already own for now but will not work correctly with newer, more modern equipment.  I can't update my hardware in the sense of downloading an update.  So I am happy that I can at least get lifetime updates, whether I need them or not, for my Sonar software.  Now if Cakewalk goes out of business next year, my "lifetime" updates will be useless.  Who knows if the next version of windows won't break sonar? 
 
The soft synth plugins of Platinum are just fine.  The main one that I use is Addictive Drums 2.  LOVE...LOVE....LOVE IT!  I do not do a lot of synth creativity, but when I do, I go to dimension pro A LOT.  I purchased Native Instruments KOMPLETE ULTIMATE and within a month, realized I dumped a lot of money on something that bogs down my system.  Does Komplete have great synth sounds? Sure.  Do I like waiting what seems like an eternity for any of the synths to load?  No, I don't.  DPro, Rapture and Z3ta load up just fine and play fine enough sounds for my sonic palate.  And these are not terribly resource hungry.
 
A good way to compare is which works better the ProChannel PC2A plugin or the Native Instruments VC2A plugin?  For me the sound so close that eq will take care of any difference.  So do I pop in PC2A in the prochannel and keep moving or do I bog my system down waiting for VC2A to verify I have a legal right to use it?  I'll go ProChannel for timeliness.
 
FX Plugins.  I've used Sonitus since forever.  Remember the ad in the movie "Crazy People" about Volvo... "They're boxy, but da.. good"  Same thing here.... "Sonitus, They're ugly, but da.. good."  I find myself using the Blues Tubes plugins more than the prochannel modules.  I liked the blues tubes so much that I found Nomad Factory's ISP 3 suite on sale and snatched up all of the nomad factory plugs.  The BREVERB plugin...I liked it so much that I bought the full blown version.  I don't have any complaints about the quality of the ProChannel modules.  They are good,  I just get lost in the collapsing and expanding of channelstrips.  When I lose my place two or three times, and I realize I've adjusted the wrong plugins two or three different times, I realize that it is just easier for me to load individual plugins and click on the plug when I need to adjust it. 

Tastes may differ but to my ear DimPro sounds aren't even near in quality to Komplete. Not that Komplete is the end to all sound quests.

Regarding Platinum's included plug-in instruments, I would add that having the full Dimension Pro and Rapture classic is a big plus.  Dimension Pro has a large sample library, and offers a lot of sound programming tools.

As Craig said earlier, Rapture is an excellent sounding synth with some very deep programming tools.  It also comes with a ton of presets. 
 
Both of these synths are great if you like to look under the hood and get your hands dirty.

True Pianos Amber is a great sounding grand piano. 

Then there are also the bundled AAS instuments:
AAS Lounge Lizard Session - Sonar Edition, with some great modelled Rhodes piano sounds.  
AAS Strum Session - Sonar Edition, which models acoustic and electric guitars, as well as chord voicing and strum patterns.
AAS Ultra Analog Session - Sonar Edition, a modelled VA synth.

Then when you consider that you also get the full Pro Channel modules and additional FX in the boutique suite, you really get a lot more content with Platinum.  I really like BREVERB Sonar and the QuadCurve EQ flyout
 
Overall I don't use all of the tools in Platinum, but I don't think I would want to give them up.  It's nice to know they are there if I ever need them.  It's a great core collection to start out with, before spending more money on 3rd party plugins 

Sanderxpander
Tastes may differ but to my ear DimPro sounds aren't even near in quality to Komplete. Not that Komplete is the end to all sound quests.

Well yup, but you're talking about another $600.  Apples to oranges ...

In a way, but the question is is it worth to spring for Platinum or better to save money and go third party.

Sanderxpander
In a way, but the question is is it worth to spring for Platinum or better to save money and go third party.

Its better to do both. I use some of the sounds in Dim Pro. I particularly like the bass sounds as well as some of the organ sounds.
 
There are plenty of other useful sounds with it. I also have Kontakt with a lot of third party libraries for it. I also have Sampletank 3. As well as GOP. Plus I just picked up Arturia's V collection. I have a few of Musiclabs guitars too. In other words I have an extensive sound library to draw from and still use Dim Pro.