I would definitely buy more shoes from vegan companies, but with my limited budget, it's second-hand or cheap shoes from target/cotton on. I guess out of the two I choose second-hand, but both positions are equally valid.
(By the way, buy etiko shoes - they're vegan AND fair trade and they so preeeety)
I personally would buy new vegan shoes as I don't like having the guilty conscience of even wearing leather. Try Etiko footwear -----> http://www.fairtradeshop.com.au/sneakers/
I think you should support imitation leather shoes and clothing as it supports the dirty chemical industries but that is not a problem as they are mostly in poor countries where they will eat or do anything just to survive.
Re the leather shoes in particular - maybe your school just hasn't thought about vegan options, and you could start something small that might help other students in future too?
When I think back on the experiments involving animals and animal parts in science class when I was in early high-school, they didn't consider vegans and vegetarians - it was gross/disturbing.