The Hyper 7 will be a LOT more durable. Infact the hyper is about the most durable buggy available.
Spares at your LHS depends on what they stock i'm afraid, but go and type hyper 7 in ebay, then do the same with XT2 and I think you'll get your answer.
I would say all buggies are the same to work on, as they all follow the same basic design.