I think I'll hit a point where I have enough but I'm just starting out now. I imagine that limit is far away.
I've noticed that I'm picky with items that I'm not collecting. Only certain cars/locomotives will do and I'll wait to get them. But if it's interesting to me because of connections to something I like in history...I tend to buy it.
I have no intention to run ore cars on my steel layout but I still bought an ore car that had Youngstown on it haha