This is a personal preference of mine, but be that as it may I shall not be ignored >:U
In my mind, I imagine there being two pools of accessories. There are common accessories that can be bought at the store, provided you have the in-game currency, and rare items that can only be won in tournaments, or for reaching certain milestones. (e.g. 25 victories in a row nets you a pair of sunglasses, or winning a match in less than thirty seconds gets you a pair [quadruplet?] of Pegasus Boots.) What I like about this is that when you encounter someone, say, wearing said pair of sunglasses, you know just how awesome at this game they are, because they're wearing that badge of honor that you know they could only get by mopping the floor with some poor sods.