[Cozumeleno]

I'd recommend keeping them for now, but collecting something else in the meantime. That way, when you find good deals that come along, you can still add to your set on a casual basis.

Once they're gone, they're gone. Not that you can't start over but your progress will be gone. Unless you really need the money, I'd hang onto them, take a break, work on something else in the meantime, and decide later.

If you still feel the same way in a few months, maybe move them then. But I wouldn't be in a rush to sell them yet - I can't tell you the amount of times I've collected something, got out of it, and got back in later.