I see music choice sort of like I see eyecandy: It can be appealing, annoying, boring or whatever else depending on one's own opinion. There are, however, some music choices that simply don't fit (use jungle.j2b in a colon level lol). The eyecandy is dependent on the tileset choice; you may or may not have made the set. The music choice is also usually from a different author. The way I see it, rating the music is not valid, but rating the choice is (if you use a "high quality" track in a level where it does not fit, then it may negatively affect the "quality" of the level). I'd say it's not something that carries much weight when it comes to rating levels, especially if you consider you can simply mute it.

I'd like it if more people use ambient tracks with realistic sounding effects such as rain, lighting, waterfalls, animal sounds etc. They tend to be quite atmospheric.