How about everything submitted has a score out of 100, and if it gets to 0 it's deleted from the server. This will not only get rid of crappy icons, but also free up server space. (add 0 to the ranking system)
Each person here has experience points. Submitting an icon/skin/etc. gives you experience. You can also get experience by voting. The more experience you have, the more your vote is worth (ie: 200 exp has less of an impact on the score than someone with 2000 exp).
To make sure people don't abuse this, you can make sure each vote is worth 2 experience, with a total of 10 exp/day.
Examples of this system:
Icon A is submitted, with an initial score of 50/100 (average). I vote 5 on it, with experience of 1000. Because of this, the icon's score gets raised to roughly 60/100. I get 2 experience for voting. I vote on four more icons, and then I no longer gain any experience for the day.
Alternatively, I vote 0 on it, with experience of 1000, and as do other people. The icon's score will get lower and lower to 0, until it reaches 0 and is deleted.
Just a suggestion.