You may want to try Titanium shoes. They are hard to get in larger sizes but are lighter than normal steel shoes and more durable than aluminum. They give you the same benefits as the aluminum and I believe they are a little cheaper depending on how difficult they are for your farrier to get.
The only class that changing to an aluminum would really possibly help in would be an under saddle class, and it only shows off the horses natural movement so if you happen to have a horse that naturally has a lot of knee action there's not a huge reason to switch from steel.
The aluminum shoes can be pretty hard on their feet also.
Good luck with your shoeing decision : )