Monster High was where things got really overwhelming for me. I'm glad I sold off most of my collection and now only have 2 boxed dolls and 3 loose. I have no regrets at all about that decision.
Basically I balance myself by just getting what I like. It's the same way with ponies. I've never had a "GET THEM ALL!" mentality. If I like the way it looks or it fits a certain character then I'll add it to the wishlis. If not, meh.