That's true, this web site exists because of the X-Tended mod and the people who worked on it (both for Reunion and now for TC). If you really appreciate both the mod and the site, donate up at the top of the page, there. I did, and I got a nice warm fuzzy in exchange.
(Plus the ability to put obnoxious dancing robots etc. in my signature.)
If you want to "buy" (support) the X-Tended mod, I think that's probably the best way to do it. I know the mod is almost released, but you can be certain that there will be a lot more work to do on it even after the first release (if the first one, XTM, is any indication). And of course we all want this site to be around for as long as possible, and it does cost money to run.
As far as doing something nice for the dev team personally... I think what they really want out of the deal is for you to play the mod and have a great time with it! (And maybe tell everyone else how awesome it is.)