I think it's only too many if you're spending money you don't have, or using money that should really be used elsewhere. Quantity is not an issue as long as you aren't choosing toys over food, shelter or caring for your family.
For me, I'm going to try to cap it at 75...It gets to be pretty hard to play with everyone! Since I like rechargeable toys, I really don't want somebody's batteries to die permanently just because I left them in storage.
However many people want or can afford is fine with me. For me personally though, I wouldn't want to own more than say 25-30. It would just become a storage issue. And I feel like if I had more than that there would be some that are too similar.