Actually, it does somewhat. Whilst I fully agree that gameplay is much more important in multiplayer than eyecandy, I've noticed that levels with memorable appearances recieve more initial attention than generic looking levels.

The initial attraction to a level is generally determined by how well the level looks at a glance. It's very difficult to determine how well a level plays simply by wandering around in for about 30 seconds. This is where the role of eyecandy comes in - it draws people in, making them curious enough to give the level a try, in order to determine the quality of the gameplay. If the level isn't fun to play in, then it's left in the dust.

Put it this way - you could make a level using Mez01 which has the best gameplay ever, but layer 8 was simply a black tile and there was literally no eyecandy of any sort to speak of. It's unlikely anyone would play that level because it just doesn't catch their eye, and they're likely to dismiss it as being bad anyway.

The way I see it, eyecandy's role is kind of the same as product packaging. It needs to be eye catching in order to grab your attention, which motivates you to play the level. Eyecandy alone won't keep your attention; that's where gameplay comes in. You may use examples like Semi/BBlair as levels that became popular yet have poor eyecandy, but remember that they're old and the standard of eyecandy found in those levels was actually considered good by 1998-2000 standards. Hell, levels don't even need to have a lot of eyecandy - a simple look usually suffices. It just needs to be an appealing look.