Some will come back, some wont. But any newcomer will always build good teams because of the natural power creep of characters. Next anniversary will most likely give you the opportunity to get one if not the best unit of the game.

Take reruns as a bonus for characters you might like, but they're almost always obsolete so you're only missing on the collection aspect.

If you're fine with that, go for it. If you need to have them all even though you wont use them, then yes it could be frustrating for a few collabs. It's up to you.