Wishing that there would be more instrumental-only sections (or wishing if he would take down the volume just a small notch) I get. But I don't understand this idea that having vocals that clash/counter the mood of the music could work (or at least, I'm not aware of any examples where it does). Smooth, crooning jazz vocalists would similarly feel out of place if the instrumentals are really rough, wild, skronky, and dissonant rather than smooth, wouldn't it?
The music of Captain Beefheart is so chaotic, unorthodox, unhinged, and dissonant that I feel like, if you're going to have vocals at all, it's got to have some of those qualities, in my mind (at a bare minimum something like a barking/mumbling messy punk vocal where the words are direct and blunt rather than non-sensical). The last thing I would want from it is clean, polished, and brimming with straight-laced meaning.
In talking about this, I'm actually becoming more and more impressed that he was somehow able to add any vocals to that music at all in a way that complements such odd music, without being devoid of artistic sensibility. Free-association phrasing that still sounds bizarrely poetic, humorous, and phonetically interesting seems more and more like the only way it could be done, the more I imagine alternatives. Maybe the sound of it can stand to be less harsh, but... I dunno.
To each there own, but I can't say I understand that.