They always say judge not the book by its cover. But, at least I know for me, I do that anyway depending if it's something I don't totally know about.
I don't really go to music stores (because most of those chain stores don't have anything good) and just pick up an album and buy it because of the cover or not. I would never solely by an album based on it's cover art. Though, some might come close. But the art is definitely tied into it. If I can listen to the tracks or at least some samples, and if I like it, then yeah I'll probably buy it. The better art it has, the more chances of it being bought by me unless the music is absolute crap or something I'm not really into (which there's plenty).
I think musicians/artists that put out music in album form need to make it pleasant for the whole experience; which includes the hardware. One may put out some good music but if the album and the booklet inside don't really have any connection with the person's music, then it's kind of a turn off (but if the music is really good, then I might buy it anyway). It's all about flow and it show flow into what you put on the album cover and such. At least, that's what I think anyway. I don't think it's too demanding to have that kind of continuity.