While X1 price will drop I don't think it will be by a lot at all. I'm sure they'll release a larger HD version in the future but I bet it will be more expensive than current.
I was going to keep my 360 but I'm lucky to have another 2 in the house (one in each of the kids rooms) so can always 'borrow' them
However, in regards to State of Decay - I liked this game and put in quite a few hours and then, well, just got bored! It all came too samey for me - people bloody whinging and having to stop the story missions to go and get more food or whatever. I think State of Decay was excellent value for money but not for me going forward.