Special uni's don't make you play better, per se. But it's exciting for the players to do something like that and I think it puts a little extra spring in their step. Plus, having those alt unis as an option is a nice carrot to offer recruits. I'll bet those players at Oregon love having so many unique options.
Sounds crazy but it can actually help with recruiting. One of my close friends is an Oregon alum and I give him crap all the time about the ridiculous uniforms they have, but he forwarded me a story once (can't find it right now) where the athletic department made comic type books of players they were recruiting showing what the player would look like in all the uniform combinations. Several of the players actually said they were looking at several schools but what won them over at Oregon was all the different uniforms. It's totally crazy, but it can make a difference.