Art Bell knows that much of what is discussed on his show is crackpot BS. He even permitted his readers to send him gag photos of Chupacabras and such nonsense.
Between the legal matter (which Art came out cleared of charges) and the BS factor, Art left the public spotlight. I believe that Rush believes a whole lot more of what he puts on the air than what Art was putting on the air. It's easier to sit behind the desk when you don't think that you are simply propagating simplemind BS about ufos, hoaxed moon landings, real moon landings with hoaxed photos that don't show the "alien" settlements, etc. I think that Rush likes his job and being able to spout his take on this issues (especially since he has an impact, even if it is not measurable, on American politics).
I've always thought of Art Bell's show as a bunch of guys sitting around the campfire, seeing who could tell the biggest lie. That's all it is, although he did have a legitimate guest from time to time. I check from time to time to see if Coast to Coast has something interesting. Something besides Bigfoot, Chupacabra, ET's, and crop circles.