I think Rincewind has undergone a little bit of character development, in that he's sort of changed from a sneaky coward, to a nicer and more philosophical coward, to a coward who does brave things because he knows he'll be forced into them anyway. Still, though, he's usually quite static WITHIN a book. I definitely think we'll be seeing less of him in the future, although he might show up for some cameos, since he's back in Ankh-Morpork and all.

I get the feeling that one appealing thing about the Vimes/Watch books is that they can bring in a lot of other inhabitants of Ankh-Morpork, and sort of use the city as a character. Of course, there are an increasing number of books that do this without concentrating on Vimes, like The Truth and Going Postal.