Unless you are disgusted by the thought of wearing animal skin, go ahead and wear out the leather products you have. There are several other threads around about the same topic, and a lot of us feel this way. Since you already own it, I personally think its better to use it and not let it go to waste. Plus, I am a college student with very limited money, so replacing such things can be a problem.
I wouldn't worry about creating demand by wearing leather. Leather coats are such a fashionable item that any of us can't really do much to add to it. If anyone asks you about what you're wearing, be sure to explain it so nobody thinks you approves. I hardly think the fashion choices of vegetarians drives the demand for animal products.