If it runs good, buy it! Not too many old boats in that kind of condition.
Check for the obvious, water in oil, trans and other basic mechanical stuff, but if you're mechanically inclined, not much easier than this to work on.
If $7k is what your budget is, then this is about the best example of what to spend it on IMO.
Doesn't matter if it's a 5 year old or 25 year old MC really as far as parts and maint go as long as both are well maintained. I would not be concerned with the old engine as long as it was properly put up for the 7 years it sat. You may be on the hook for some little stuf like rebuilding the carb, fuel pump, etc. When I bought my 06 in favor of my 96 model, I put just as much work into it, probably more, but the new one has more bells and whistles.
'06 X2 MCX
"I understand why some people may not want to do this the way I have recommended but I can't understand the death grip some people have on a toilet plunger with a hose fitting." -JimN