For me, stash growth is an organic thing, never intended.
Almost every kit I buy is the must have, can't wait to build type of thing. But then when I start it, whether it's the research stage or actual build, I'll inevitably come up against a waiting period, whether it's AM parts or paint and then that opens a door for something else shiny to come along.
Then there is sub trends I get stuck in. I'll on an off chance build a Fine Molds, Fujimi, etc and be so impressed with it that I'll pick up a few others.
And then on top of that, there's the round it out to get free shipping type deals where $20 more will get you off the hook on $15 shipping, so another kit falls into cart.
I probably have about 25-50 models in buildable condition, that number again in stuff that's been moved to the basement and rummage through by my sons.
I've successfully gone through year long periods where I haven't bought any kitsuntil I finish a number I have, but in my household, things get budgeted (kids, retirement and college costs and all), so money that is put aside for hobbies will disappear if not used. When not buying kits, it'll be tools.
I'd love to be able to build, buy, build like I did as a kid. It was Saturday morning on the Schwinn Stingray to the LHS, race home and start glueing, the thing done by Mutual of Omaha's Wild Kingdom on Sunday night. Logistics just work against it now in the cluttered grownup world.
Will all the research, AM, etc that goes into my building as an adult, my favorites always seem to be the one weekend and done OOB type.