Sierra......I can't see the unmeasurable performance difference in an aluminum sprocket being worth the extra dough.I am pretty sure the front sprocket is only available in Steel. There is a boat load of force on the front sprocket. The rear is larger in Diameter and has less ft/lbs of force. Hardened 70XX series aluminum or better should hold up OK. Many people won't use anything less than steel rear sprockets to prevent fast wear. Aluminum has less rotational mass and also less unsprung weight. What is your preference? Less maintenance or more performance?
You should get a copy of the shop manual if you like to wrench on your own bike. They are really good. It will walk you through any level of repair up to a complete rebuild.
Tell me if I'm wrong.