It depends on how the game is setup. If it's "almost possible" to get them all, then it kind of feels like you have to get them all, even if that involves some serious work. This can be compounded if certain "best of breed" types can only be obtained in certain areas, or at certain times.

However, if it's setup so that it's basically impossible to get them all, but you can get many or any, then it doesn't feel as bad, especially if trading is an actual option that works. If the special and/or limited ones are more cosmetic, it becomes less of a chore and more of a "look what I have".