It's not always just the representation of the packaging that is nice. It's also perhaps the idea that the artist themselves put a lot of work into it - the images, the artwork, the lyrics layout and the fonts, the liner notes or stories contained within, and of course the credits/thank-yous.
Practically speaking, though, how likely is it that the artist actually put in all that work? I don't know for sure, but it seems far more likely to me that a typical musician, not being familiar with graphic design, would just relay the intended style to a professional who takes care of all that independently. Actually, I don't even see why the musician would do that; I would think the label would take care of all of this dirty work, with little intervention by the musicians. It's standard practice for artists to select album artwork, sure, but with regard to everything else, the Steven Wilson "complete package" approach is a very rare exception to the general rule.
Now, I'm too young to have lived through the vinyl days, so perhaps things were significantly different back then. However, these days, I think I'd find myself disappointed more often than not if I bought a CD intending to greatly enjoy the packaging. Sometimes the booklet is full of excellent art, but just as often it's black lyrics on a white background (and sometimes I don't find any lyrics at all).
While it's possible that bigger artists who succumb to their record company's whims may often let them take care of the packaging, it's also possible that they DO put their opinions in on what they sell. At least, the artists who care about what it is they're selling SHOULD do that.
But, for what *I* listen to and collect and keep, it always seems that the packaging is an important part, and that the band/artists does keep a close eye on what it is they're releasing, bands like Rush or Dream Theater that have some say in the art direction of their products and packages.
Sure, more often than not, an album's package may be plain or only contain lyrics, but that's at the loss of the artist - there's a great opportunity there to tell the listener/fan "Hey, here's some stuff that is relevant to what you're about to listen to, so pay attention and enjoy!"
If an album is lacking in that sort of thing, it's truly a sad statement. Then again, most of the people who don't care to have all of that probably don't even bother to put album artwork with their mp3s on their player/iPod. I've seen plenty of friends' iPods and their songs don't have artwork and I give them a blank-stare as if to say "Uh, why don't you have artwork?" and they don't care....and that sort of thing bugs me. These are also the same people who don't properly categorize their songs, either including misspelled titles or names, wrong track numbers, wrong genres, etc. etc. and THAT really bugs me.
Then again, I'm a little bit OCD...so...
-Marc.