"One man's junk is another man's treasure". What one person doesn't find useful, another person might find very useful. That definitely shouldn't reflect the actual quality of the work.
At the same time, I find these ratings completely useless. I don't look at ratings to determine whether or not I'm going to use an addon. I look at what it does for me and how well it does it. The only way to really find that out is to try it myself. As for Shelley's suggestion, I think the idea is going in the right direction, but I don't think I'd personally take the time to rate a product on various different levels. I either like it or I don't. And trust me, when shopping online, I've purchased a product that had all the stars in the bloody universe and when I received it I was greatly disappointed. It's just not an accurate way of measuring it's quality.