I'm one of the rare few that actually doesn't mind the default Unit Frames that much, what I dislike though is that you can't see pet/party buffs/debuffs unless you mouse over the frame, I also dislike that the default Target Frame doesn't show all 40 debuffs.
There's an addon called Unit Frame Buffs that fixes that but come patch 3.0.2 this addon will stop working due to the secure template changes.
I am in the same boat as you, though I had never been able to find an addon that did this. Now I have found one, but it's broken :) I hope something can be done as well, unfortunately I myself am unable to do so.
I don't know of anything that will work in WotLK that also doesn't change the unit frame appearance... but if you can stand a new look for your frames: X-Perl allows you to see all the buffs and debuffs, as well as change the sizing on them.