It depends. For those of who enjoy the "collect" part of the hobby, and enjoy spending time watching the market, making deals, picking up new and rare stuff, it's never enough. My collections is split pretty evenly between guns I shoot and I guns I don't, and also guns I will keep forever, and ones I'll sell / trade when i feel like picking up something new.
I probably have a "medium" collection, and the current size is limited by how many I can store in my safes.
Ammo and magazines? Never enough....N+1