The difference between studio and producer seems to be mostly a small suit of plugins, console emulators, tape saturation, etc.
 
I am playing with the demo, but mostly just learning how it works, not doing any audio production.  I have k9U suite of plugs, is there anything in Producer that will be value added, or should I go with Studio?   Is Producer's mastering suite pro, or are most people using 3rd party plugs?
 
Having tested Producer over the past 2 days, the thing that stands out is that the UI is really good, worth the price of entry.  Some of the X3 reviews have said the basic plugs are not great.
 

Well I don't know where you read that the plugins in Sonar are not great. They are. Many are unique and all are of a quality that is every bit as good as many third party plugins.
 
I do believe you will want to add to what CW has both from them and others. For example Kontakt is the single best sampler around. I mentioned in another thread about the Moog Modular V from Arturia. Those are the best of their type. But Dimension Pro will hold its own with many. Then the effects that are bundled with Producer are in a word outstanding. I like the Pro Channel modules and have all the CW ones and some third party ones. Over all if someone is disparaging of the plugins that come with X3 Producer either they are talking through their rears or they have bought a hold slew of third party plugins that they do not want to admit to their folly.  
 
 

I have X3 Producer, and also like the bundled plugins, as well.
 
It's a really nice package.
 
Bob Bone
 

This is the review I read about the plugs sounding "dated".
 
Google SONAR x3 Review PCMAG

There is a certain irony in the plethora of vintage styled plugins saturating the market and the idea that a plugin sounds dated. I think the only plugins that is even remotely true for is preset romplers in relation to sounds used in current pop misic. How does a compressor sound "dated"? Especially since the compressors in the pro channel are vintage emulations.

Very few bundled plugins in any DAW would compete for "absolute best of its type" compared to third party plugs. Does not make them bad. When a company makes a plug it thinks is on that level, they often offer it as a third party plugin to be used in other DAWS like was done with CA2A. Cake plugins are there to offer the user the value of quality plugins that will get the job done without third party plugins if it comes down to that.

Teal
This is the review I read about the plugs sounding "dated".
 
Google SONAR x3 Review PCMAG

Well that is referring to Sonar X3. Not Sonar X3 Studio or Sonar X3 Producer. In the past we viewed the entry level version as good value but with no bells and whistles. I was all set to find fault with them but with the version they are reviewing I have little doubt that the meager plugins in that versions won't impress anyone. For me I don't think about that version much. Never have. Its abetter value thane it used to be. But before X3 there were only two versions that had the full measure of features. The was Sonar Studio and Producer. Producer had everything CW had to offer. 
 
If you are thinking getting the base version of X3 it wont have all the plugins that Studio or Producer come with.
 
When I talk about Sonar I am talking about the Producer version only. That is the version I have always used.  

To me, when people say they need better plugins, than those offered by Cakewalk, is akin to saying I need a better mics than my sub $1k mics, like my EV RE20, Beyer M160, my single pattern Neuman, etc, etc.
The problem is the ears of the operator, not the available options.  "If I don't have the expensive Royer 122 version to record my guitar, it'll never sound good..."   I repeat myself...the problem is the ears of the operator.  
Besides...how can you tell listening thru your "KRK Rockets" ?? (or similar $200/pr speakers)

The CA2A is outstanding.  The PC4k PC modules are outstanding.  Breverb is outstanding.  The PC EQ is outstanding....  Move your mic 2" and hear the greater difference.

Teal
This is the review I read about the plugs sounding "dated".
 
Google SONAR x3 Review PCMAG

He's reviewing the $99 version. Check out the feature comparison chart for the three versions - it's $99 because it doesn't have all the cool plugs. However, it has all the cool technology features, which is probably why the review is so extremely favorable.
 

mixmkr
To me, when people say they need better plugins, than those offered by Cakewalk, is akin to saying I need a better mics than my sub $1k mics, like my EV RE20, Beyer M160, my single pattern Neuman, etc, etc.
The problem is the ears of the operator, not the available options.  "If I don't have the expensive Royer 122 version to record my guitar, it'll never sound good..."   I repeat myself...the problem is the ears of the operator.  
Besides...how can you tell listening thru your "KRK Rockets" ?? (or similar $200/pr speakers)

The CA2A is outstanding.  The PC4k PC modules are outstanding.  Breverb is outstanding.  The PC EQ is outstanding....  Move your mic 2" and hear the greater difference.

I was a SONAR user of old, I was using CWPA6 through SONAR XL, and honestly one of the big reasons I switched to the 1K Samplitude back in 2004/5 was that the bundled plug-ins were pretty excellent and comprehensive.  Back then good plug ins were not common except Waves or UAD1 which were both very expensive.  Everything I did just sounded better in Samplitude. In the 32-bit days it was absolutely the best sounding mix engine, not sure thats true today.
 
So my question is not about not knowing how to use tools or wanting better than stock plug ins, its about if the stock plugs in Sonar X3 are placeholders or are they pro?  Keep in mind one of the reasons I left the platform was the realization that the plugs were poor quality.  Native plugs have come a long way, just want to know if those advances made their wy into X3.

If you want a much more complete picture, may I suggest you search these forums for more information. Almost every question you've posed has already been answered (except for the RME one because no one has encountered that problem). There are multiple threads about the plug-ins with a huge variety of opinions, comparisons to Waves and other third party plug-ins, etc.; these threads have developed over days and even weeks.
 
As to whether the Sonitus plugs sound dated, the only one that sounds "dated" is the reverb. I'm really not sure how something like a delay can sound "dated." A signal delayed by 126 milliseconds in 2014 sounds the same as a signal delayed by 126 milliseconds in 1999