Is it even worth it to buy a 360?

I was thinking of buying an Xbox 360, and all I would really use it for is Rockband 2 and Halo 3, with Xbox live, of course. Now, my only concern, is that I'll pay like $500 for all this, and then in like a month, Microsoft will release a new console and make the 360 obsolete. What's the possibility of this happening? Some people told me it is likely, others tell me that it'll take years before the 360 fades. Anybody know for sure?