A 2nd set of wheels is a good investment and will continue to serve you well even if you upgrade bikes later.
That said, stock Giant wheels are actually decent wheels, so you might be even better served to drop a few dollars on a fast set of tires. That can make a BIG difference in speed and handling.

Whatever you do, don't try to do too many upgrades too soon. If you really do take to cycling, your ideas about what kind of bike and gear you want may change two or three times in the next year or two. You don't want to spend all your money on a great touring bike only to discover you're really a CX racer at heart. By the end of the summer you'll have a much better idea of what you like and don't like on your current setup and won't need us to tell you where you should spend your upgrade bucks.