Is a 40 foot fifth wheel too long to access neat places?

Depends on where you go...a forty footer would look like a matchbox car in the desert Southwest. No problem with access/parking in places like the vast, open BLM lands around Quartzite, for example.

But if you intend to venture into the more forested lands of, say, the Pacific Northwest, I think you'll find your choices much more limited. I've camped all over that area and can think of few secondary or even primary Forest Service roads suitable for a rig that size.