I'll probably break down in another month or so and load up a few basic mods: an auctioneer mod, my favorite unit frames and hotbars, and maybe a tracker or two if I'm working on anything involving repetitive farming and travel. Other than that, I find it helpful to fly light as I hop between characters with drastically different approaches to the game.
I used to mod my UI heavily, though, and I know how addicting it can be. I would compare it to a painting you never finish adding to; my husband might imply it's more like a scab you can't stop picking. Where do you stand -- are you a dyed-in-the-wool modder? Do you enjoy adding a few utilitarian touches to your UI, or is redesigning the entire look and feel of your display more your style?