Agreed. Much as I love Hammer & Tongs and a lot of the movie's visual design (at least, until the point where it became obvious they ran out of money), the script went straight to hell as soon as they got off the Vogon ship.
I've seen this thing a million times. I've been watching it since I was too young to really understand it. But I've always remembered the babelfish argument. When I finally read the books, this guy was always the voice of the Guide, in my head. Actually, his was the voice of the whole series.