My school didn't have uniforms, but I wished that they did. I went through an awkward phase from about 7th - 10th grades where I didn't like shopping and so wore horrendous clothes that didn't fit properly. Also liked high ponytails for a while, emphasizing my huge forehead and breaking so many of the hairs on the top of my head (due to the weight) that I had a sort of halo.

I think that either way, the kids are going to turn out fine (in most cases), and it just depends which pros and which cons are more important to the school. I'm pretty sure the rich and poor kids would still be obvious from other factors - hair, teeth, make-up, etc. - but at least the teachers wouldn't have to be policing the dress code anymore. (Tank top strap width, skirt length, t-shirts with writing, all that.)