I think the style factor comes in most during tournaments. It may be just a psychogical boost you get from feeling prepared but every little thing helps. The intimidation factor usually only comes into play in local events or against teams who aren't too experienced.
With the increased popularity of jerseys and such, I've found I like dressing down for practice and pickup games. I played most of the summer in a Tshirt, while most others were in jerseys. If anything, I think I played better because I was more relaxed and felt more comfortable (I'm a jeans and Tshirt kinda guy)
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In the end, it's whatever works for you. If a new jersey or the latest stylin' headgear makes you feel a little more confident, a little more aggressive - that can be the difference between a good day and a great day.