After the drydock indulgence, the V'Ger shots get diminishing returns because the point's been made already. They don't contribute to the story, except to say that V'Ger is really big, intricate, and weird. That point could have been made more efficiently.
I've never felt that way. For one thing, it's a chance to sit back and listen to one of the finest musical scores in motion picture history without a lot of dialogue and sound effects getting in the way, and there's nothing wrong with that. For another, the V'Ger flyover features what are still some of the most amazing, beautiful, spectacular images I've ever seen on the screen, a real triumph of design and FX technology. It's the closest thing I've ever seen onscreen to the sense of wonder at superadvanced alien technology that you get from books like Rendezvous with Rama
I was speaking from the perspective of the general audience. Even though I personally enjoy the V'Ger shots, and the music, I can fully relate to the diminishing returns aspect. I believe it applies in this case from the perspective of the general audience.
Trimming the V'Ger scenes by one minute or two doesn't change the fact that, to a general audience, the middle part of the film is boresville.