Plugin Overload: Which FX/Virtual Instruments to use and which are old?

I understand option overload! However that's kind of like saying "I just bought a set of 200 colored pencils, which colors will I not need?" You may not use Carmine Indigo a lot, but when you need it...
 
Case in point: A recent thread about how in a shootout with all drum modules a user had, including AD2, the "Loose Kit" in SI-Drums sounded the best for his application. And while I use the QuadCurve as my go-to EQ, some of the Blue Tubes EQs give different colorations, and the Sonitus has some features other EQs don't have.
 
Another reason for all those plug-ins is for those with legacy projects and who need the older plug-ins. For example Rapture Full has great editing capabilities compared to Rapture Session, which is more of a ROMpler type of VI. Although Rapture Pro replaces both Dimension Pro and Rapture Pro because it can load presets from eac and has extensive programmability, not everyone has it. 
 
Because plug-in usefulness is so subjective probably your best strategy is to try them and if there are plug-ins you don't think you'll use, exclude them in the plug-in manager. But even old plug-ins have their uses. For example, there really wasn't anything like Cyclone or RXP Player until a much later version of Reason appeared with OctoRex. If anything, I think many older plug-ins are unappreciated because they're "old." I see them more like "ahead of their time."

A couple of features Session Drummer has which AD2 does not
1) Session drummer can map one or many samples to a drum pad. AD2 only plays AD2 kits.
2) It is possible to interactively play MIDI clips with Session Drummer.
 
Rapture Session also contains a collection of programs and samples from Rapture Pro which are not part of Rapture. Rapture Session can replace the 32bit Cakewalk Sound Center; convenient when running 64bit SONAR.

That's the way I tend to work too, but the other day I was having trouble with a dull vocal and I slapped on some old Pultec style plug I've had for ages and don't use that often (I think Waves), picked a preset and blammo, instant magic. You can't always say stuff is obsolete just because it's been around for a long time or there are more advanced plugins available, is all I'm saying. It's fine to have something to start with and you can base that on other people's favorites, but the real trick is learning/knowing what you have and finding the right tool for the job.

Agentcalm
Howdy y'all
I know this isn't really answering the question but on a side note, i tidied up all my plug ins into categorises which has helped a lot.  Instead of a long list of hundreds of plug ins, i have them listed as EQ, Compressors, Time Based (delay, reverbs etc).    I know its a little off the subject but a tidy list of plug ins does help a lot. 

Spot on - organization really helps, whether by function, manufacturer, or whatever works best for the user.

"They're not old they're vintage!" 

I guess it also depends on if you are using a laptop or desktop.  Sonar, Studio 1, and Live Suite can use a lot of space.  I store everything involving samples on another drive.