I try to keep a 2 car rule.. It might be 3 for a while, but then 1 gotta go hehe..
It`s not that i havent got the money for more, but it keeps the hobby room tidy, the wife happy(ish), the cost`s goes down (since i gotta sell one to buy one), and perhaps most important; i havent got time for more anyway ;)
When i get bored of one, i sell it and get the joy of buying a new.
The modded E-revo BL is on top of my list right now, but havent owned it more than 4 months yet. (just got back in the hobby after a couple years of changing diper`s and wrenching 1:1 turbo`d streetcars...).