I prefer not to work with steel, for a few reasons.
One being aluminun alloys can be left as is without plating. Plating can be a hassle.
I think most bike parts should be lighter, and stronger than stock parts. In the case of motormounts, they may weigh around the same as stock, but be much stiffer.
The lighter weight thing was important on the frame kits I built, I find it hard to add weight to a hopefully high performance bike, a step in the wrong direction it seems.