I am still using my XP-1 as my only camera, I don't think I'll be upgrading to the XP-2 when it gets announced either for a couple of reasons.
1. It's not that I don't suffer from GAS, I suffer from GAS as much as the next person, however my XP-1 is really more than adequate for my skill level, and realistically I don't think getting an improved camera will really make me a better photographer or more succinctly my XP-1 does everything I want it to do and then some.
2. I'm probably looking at things from a Leica perspective, If you have an M9, is it really advisable to upgrade to an M9-P? or to an M240? I don't think the focusing will get any faster
, there will be some minor function upgrades and additions, but do you
really need these to take your photos? I'm probably risking comparing apples and oranges here, and I know that the focus speed of the XP-1 has been the subject of many criticisms and I will admit that to some will not be able to live with it's focusing speed, but for me it has been more than adequate and I've shot low light, street, landscapes, candids, etc.. and it has never let me down, I guess it'll come down to how you shoot.
3. The upgraded sensor could be tons better than the XP-1, but I can't remember the last time I printed a billboard sized photo, actually I can't remember ever printing a photo larger than 16 x 20 with most of my photos ending up in various forums and flickr online. If did photography for a living and I am being commissioned for a job then it'll be another story.