It's not just the plug ins in my opinion.
Its the Region FX. I use all 3 of them and often. those 3 Region FX right there is what makes sonar unique from the other DAW's.

dwardzala
The plug-ins included with Sonar are good.  You can get pro sounding recordings using them if you know what you are doing.
 
Some of the third party plugins are great, but you still have to know what you are doing to get pro sounding recordings out of them.
 
In other words, you don't need to buy any additional plug-ins to get started.  You may decide in the future that you want to, but Sonar Platinum has everything you need.
 
Also, even though you didn't ask, the same is generally true with their included virtual instruments.

+1  Well put.

The only plug-in I find lacking in SONAR is a good multi-band maximizer, but if you're willing to make the effort, you can fashion one out of multiple LP MBs with each one followed by a Concrete Limiter (a ProChannel module I highly recommend).
 
As to your original question, no less a luminary than Mick Jagger himself answered this question many years ago...apparently he could see into the future, and saw what SONAR would become:
 
"You can't always get what you want.
But if you try sometimes
Well you just might find...
You get what you need."
 

Such great answers, thanks folks. I guess I'll just sit tight, dig in and learn all I can with what I have already. Heck, I still don't really know all I've got at my fingertips as it is

Are there by any chance any other tutorial or freeware SONAR projects out there on the net to home my mixing and mastering skills on?

http://www.discmakers.com/pdf/cakewalk-guide.pdf
 
It says for X3 but since it relates to the ProChannel, it's still relevant.

Groove 3 has a decent video on mixing in Sonar (I think its even for X1, most of it still applies).its got some great fundamental tips. It goes through and mixes a whole song (Rock) 1 track at a time.

Thank you for this, much appreciated.

All to be fair, I know how to mix - I just don't know how to mix if that makes sense. I took the X2 course out at Lynda.com by Garrick Chow and it gave me the lay of the land pretty well. I understand things like panning, EQ and levels but the tricks are in the best ways to use these things. This is where I am at present and at least it's a fun journey lol

"how to mix" is something I hope to continue to learn until I'm no longer walking the earth. 

This is interesting. I always kind of thought a compressor was a compressor was a compressor, except for layout and so called workflow. I hear you saying they sound different and that one may be better than another for a certain sound. I've got a lot to learn!