Here's what I have discovered.
Cake comes with a variety of synths, most notably the Cakewalk Sound Center. Cake includes quite a few sounds and then sells additional sound packs for $20 each. They also include some additional synths in some of the new versions of Sonar and Cake products......bass, drums, etc....
These all have a very reasonable sound, quite useable for 95% of the applications I would use them in.
If you buy some of the 3rd party synths and samplers, pianos, bass guitar, guitar, etc..... most the the ones in the "affordable" price range are the same quality as the ones Cake gives you for free or in the packs for $20.
Next step up: Native instruments also has some very nice and superb sounding sample libraries. I consider them a step above the Cakewalk $20 sound packs and really not that much of a step up IMHO. Worth the price since the Komplete Collection is definitely a "must have" for anyone using synths and samples.
To Infinity and beyond: Once you step out and spend the upper 3 digit range and into the 4 digit range $1000+....NOW you're getting into the sounds that will knock your proverbial socks off. These tend to be the samples that even a player can't tell the difference .... is is a synth sample or is it a real string section?...... However, unless scoring film is your livelihood, and it provides a regular paycheck to you, using those libraries is generally not in the interest or financial reach of the average hobbyist.
I had the typical case of GAS for a time..... I have a bunch of VST's & FX that I rarely use as a result. Some free, some not.
Just my random thoughts on this topic of G.A.S.