In the beginning we're understandably a bit voracious, but the more we add on the table, the more discriminating gourmet we become.
-- Sweelinck
Never more true words, I am definitley becoming a discriminating gourmet, I even feel like my module-buying is slowly coming to an end.... Shocking I know
-- wishbonebrewery
When I first got into this, I wanted every module out there. As my collection grew, I started being more cognizant of function overlap. No need to get a module, no matter how pretty it is, if all it does is perform the same function as a module I already own.
The big change for me came when experimenting with patches and I learned what I see as one of the most important rules in eurorack, "Turn the knobs slowly, real slowly." I had a tendency when playing to make these big moves, testing the extremes. It's when you make small control changes that you really learn the module and find all kinds of sweet spots (waves going into phase, amplitudes mixing at just the right level, etc.).
After that I was finding features in modules that I didn't know were there. Now every time I see a new module, I think of all the little extra features my exisiting modules have and I consider if I can already do, with one or more currently-owned modules, what the new module does.