Cast aluminum wheels are not that much lighter than steel, there's typically only something like a 3-7 lb. difference between them and steel wheels which doesn't really make a significant difference. Forged aluminum is lighter since it can be made thinner but being forged makes them a LOT more expensive.
To me, the 3-7 lb. difference per wheel is insignificant and not, by itself, a reason to switch to aluminum. There are other benefits like steel being far easier to dent and bend but if making a change, understand that performance or better braking is not going to be significantly better with aluminum. What makes the biggest difference in performance or braking? The diameter of the tire. The bigger the diameter, the more leverage it has over both the engine and the brakes.