I would agree that what you '
need' you already have for the most part, except maybe some specialized stuff. As you grow you will undoubtedly experiment and gather a larger arsenal of tools, and like most, far more than you need. I never really used any of the Sonar supplied stuff outside Pro Channel, I did mess around way back with some sonitus stuff, or whatever they are called, but I just didn't get on with them, something never clicked, same with the tools that came with REAPER, it's all there, all you need, but I just didn't click with them, look/UI whatever (look isn't probably a good reason to discard something . . . but) it just didn't happen.
I went through trying heaps of different stuff, Melda and Fab Filter Total bundles, Toneboosters, T-Racks, Izotope etc etc, until Waves ditched the iLok, then I tried them, love them to death, if it wasn't for Ilok I would climbed aboard the Waves boat long ago, and for me my search would have been over and I would have saved HEAPS of money. I'm lucky in that the money side of things is of no concern, but I still don't like just throwing it away. Now I just use Waves pretty much exclusively, along with Izotopes Ozone 5/6 Advanced, Alloy 2, Nectar Production suite and maybe some other stuff now and then like the T Racks stuff, but not very often. I ALWAYS use the Sonar quad curve in Pro Channel on the master track (sometimes others) because it just adds something very nice, easy to use, and it
really is nice.
I could recommend heaps of stuff that
I like and think are great, you may not. I can recommend the ToneBoosters catalog, the are very nice plugs, and cheap, you get the lot for not much over $100 if memory serves, Izotope's stuff, more expensive, but good all in one for mixing and mastering. There are also heaps of free stuff like, Tokyo Dawn Labs eq and compressors, Mercurial, Ignite amps, Lapou and TSE for guitar sims and effects, all excellent stuff, there is so much out there.
Mess around with what you've got, try out some of the freely available stuff, some of it is
very good, and worthy of the task, and by all means, if you can and have the desire try some of the commercial stuff, if there are demo's, put them through their paces before parting with your cash, and try a few different ones before you do, don't just settler for the first one, you may find something that just gel's with you, just clicks.
Most of all have fun