One thing that seems to work for me (relatively) is that I try to determine what I need and stay focused on that.
I have a lot of plug-ins which I just never use, which I bought because they were on sale, many that were a cheap alternative to this or that, or to make up for this or that, and such.
For example, I had been after a SSL-type of channel strip for quite a while - and I've spent almost as much on alternatives as it would have cost me to buy the Waves Bundle (on sale). And the thing is that, I still wanted the Waves bundle.
I did eventually end up grabbing McDSP's Channel G
, which I actually prefer to Wave SSL. But the lesson I've learned is that it would have been much wiser to buy Channel G in the first place than to spend money on plug-ins I wasn't 100% happy w/, anyway.
These days, I try to plan ahead, based on my needs. Like, I know I'm doing a lot of manual level editing on bass, so Waves Bass Rider is on my list, but I have other priorities. C4 is also on that list, because I'm not too happy w/ the multiband in Logic - but I'm giving myself a bit more time w/ it, before I buy the C4.
But overall, even just $100 spent on plug-ins is $100 that I can put on Roxul for bass traps or on a new pick up for one of my guitars - something which makes a much bigger difference than plug-ins, considering that even just the basic bundles stuff that comes w/ any DAW these days is fairly decent.