I probably acquire about 5-7 kits a year, WWI aircraft and other subjects - mainly ones that take my fancy, that I find aesthetically and/or historically interesting - some I buy, some are gifts. I build 4-5 a year I reckon, maybe 6 at a push, so my stash is growing slowly. Each time I get a new model I think I will build that particular one next but never do! If I could perceive a situation where I knew I would have the time to finish everything then I'd probably buy more kits.
I reckon I have 25-30 in the stash, not counted for a while, with maybe 8 WNW plus I think 5 other WWI aircraft. I have a couple of WWII aircraft, cold war fighters, modern helicopters, and a few vehicles from Revell (old cars, and the classic London Routemaster bus).
This weekend may see my stash grow when I visit the RAF Waddington Airshow. There are usually several model stores there, some selling kits you rarely see in the LHS, that you can only get online, but nothing beats looking at the box in the flesh, and even inside if not sealed. Some stalls have offers, for example last year I got the Trumpeter Me-262 in 1:32 for £25 that should have been £50. I think that is part of the psychological issues - the kits are there, I am there, the prices are attractive etc..