One of the things that really bugs me is content that looks bad or amateurish. I don't think that looks can change the essential nature of a piece of content.
Bad content is still bad regardless of how pretty it looks.
Looks do, however, have some bearing on how seriously a piece of content is taken. If a well written or particularly interesting piece is presented in amateurish or simply ugly way, I may just skip it without bothering to find out if it is good. On the other hand, a well laid out piece of crap may get the chance to waste a few minutes of my time.
The care with which something is presented says a lot about how much the presenter values it or about the skill of the presenter. Something that looks thrown together or looks like it was pooped out by a some kid with a free Web publishing kit, why should I take it seriously? The person creating it didn't.
This is much worse when it is done by professional companies where their is their knowledge and experience. If the documentation is laid out to look like something out of the 90s or has the worst qualities of print with none of the Web goodness, what does that say about the quality of the content?
If the content lacks even the basics for ease of access, why should I trust that I will be rewarded for my struggles to find anything of use?