Josh Putnam has an interesting item up about talk within the GOP of finding a way to limit debates during the next nomination cycle. I agree with him that it's unlikely that they'll wind up doing it through the rules.
He also walks us through some of the incentives. As he notes, frontrunners presumably prefer to have few debates; longshots want more. It's also true that minority groups and factions within the party might prefer more debates; they give those voices within the party an opportunity to be heard.
One might also say that the candidates as a group might have some interest in having the party clamp down on the number of debates. There's a bit of a collective action problem here. Candidates, regardless of their strategic incentives, are known to not especially like having a schedule dominated by debates, but they of course have strong incentives to show up once someone schedules one.
Meanwhile, there's the problem of crank "candidates" who basically have no real interest or chance of winning a nomination but are primarily in it to win a Fox News contract (or MSNBC show). The problem for the parties is that the debates tend to be the face of the party (especially during the year before Iowa, when there's no election results to drive the coverage) and a few of those crank candidates can really distort the party's image.
As far as the incentives to hold debates: in addition to interest from trailing candidates and crank candidates, there's also the interest of host groups (who like the attention, whether it's local parties or universities or other groups) and the TV folks, especially the cable news networks, who get inexpensive, relatively high-profile programming.
Against that, in addition to the frontrunning candidates who don't want to give their opponents a platform and the (real) candidates collectively who don't like doing to many of them is the interest of the party, collectively, in the free publicity. After all, if you actually are putting on a good show, it presumably is going to make the party look good!
My guess is that you would find the parties' attitudes towards debates totally dominated, then, by their impression of how the last round went. Sometimes (Democrats in 2008, perhaps Republicans in 2000) the debates are perceived as successful. Sometimes (Republicans 2012) they are not.
But getting back to Josh's point...when you have something like this where the parties' perceptions change from cycle to cycle, it's really unlikely that you're going to get reform by rules. After all, it's hard enough to come up with rules to push the caucuses and primaries back, and for that one the party-as-party has a clear and consistent interest in doing it.
And the real important thing for the Republicans, it seems to me, is to figure out some way to either get those crank candidates off the stage or, at least, make them behave themselves even though all the incentives for them work the other way (how do you get a Fox News gig if you don't say outrageous things?). How to do that, however, I have no idea.