I agree with the consensus; get the longer motorhome if that's what you really are interested in. I don't think the extra six feet will too often mean not being able to get a site. Of course, it does mean that fewer sites will fit you, but at least in my limited experience the two basic conditions seem to be "pretty much nothing is available" (in which case one is out of luck regardless) or "there's at lest something available for various sized RVs."
If you're willing to be somewhat flexible in terms of where you end up going and what ammenities you require, or else to plan farther in advance for things you don't care to be flexible about, you should have few problems at 30'.
Here in Vermont, we may very well have the fewest large sites proportionally of any state park system. I have yet to encounter a time when I wished to go camping in my 32' class C when I couldn't find a suitable site at a state park, even on short notice (a couple days or the same day). I have sometimes had to be a bit flexible about which state park I camped at. When traveling out of state, the main problems I've had are more along the lines of pulling in to a public park and finding it's closed for rennovations for the season or something like that.
