Matt Smith is my favourite doctor (Though it may have a lot to do with the interplay with Darvil and Gillan), but I don't really want to see him be back for more than possibly a multiple doctors-thing. His story is more or less done, and it makes no sense for the doctor to take the same face again,
My sentiments exactly.
Ive always thought that the only possible reason they'd bring back a previous actor to play a new incarnation was if the show was struggling in the ratings and needed a boost. Like how they considered bringing Troughton back as the Seventh Doctor. But it would be just as easy to instead cast a big name to pull in ratings. Though I wouldn't rule out the possibility of them doing it some day.