This is a difficult subject. To some ratings are important, if for no other reason that it effects what visitors see, so I try to rate the ones I download. There are some stunning skins which I wind up not using very much because they are not (for my eyes or because I find them distracting) to me for eveyday use. I wouldn't rate them less for that. Similarly there are some more subtle skins that while not flashy or intricate I really enjoy and use frequently. And appreciate more as I use them. Often they are not generally rated as highly because they are not as much of a "wow" upon first glance to look at.
Just because something is not to my every day personal taste I don't downrate it for that. For example, there is some artwork in museums or galleries I may find amazing, but even so I wouldn't hang it (or a replica) in my house.
But every once and a while the subject comes up here and a skinner may say, "how can people rate so high these skins that are tchnically bad, the graphics are put together as they should be, etc." I suppose the skinner took the other skins apart to see and came to those conclusions. I don't know if they're talking out of their hat or really do find things technically wrong with the skin. What I do know is that I am not a skinner and I don't see those things, unless it obviously effects how the skin works on my PC. If the skin works and looks good that's OK for me. But my point is, those comments make me feel as if I shouldn't rate skins at all because I am not a skinner and don't know the technical stuff. Then I think perhaps only skinners should be allowed to rate each others' work and perhaps I shouldn't rate anything at all. (Even if something has been rated low that I think should be higher.)
Some authors complain about not getting rated or not rated as high as others. Some even get into how many downloads there have been compared to others. Others ask primarily for comments to see how the skin plays, are there suggestions for improvement, etc which makes sense to me.
I do think, however, if I were a skinner and put that much effort into it I would be doing it for what I want to do and not to play to the audience for the number of downloads and/or ratings. If I were to be paid for it then that would be important. But when it's not, I wouldn't spend effort putting together something I'm not that interested in simply to post it and play a popularity game with ratings and downloads. If it's about the work, then that is the focus. If it's more about measuring oneself against others' "popularity" well that's another issue IMO.