For a 2nd tier division the Championship gets a fair amount of exposure anyway and rightly so as it is not only better supported than most top tier divisions in Europe but also offers a better quality of football than most of them as well.
As KR says, having clubs such as Newcastle and Villa in there will bring added exposure but I do feel that the Rafa effect will add to that slightly, particularly as him staying is likely to mean their better players also remaining
I was a Newcastle fan I wouldn't be booking any train tickets in advance next season. They'll probably have at least 70% of their games games moved for Sky. Based on the players I've heard them get linked with (Agger, Carrick, Crouch etc) I'd be shocked if they didn't win promotion.
Yes of course he'll bring more exposure but that's not to say the Championship doesn't have a lot of exposure already. I think it's great for the league, a huge reminder of just how big the Championship is now.