How much of the weight on your current bike is the frame? Given the mark-up you're seeing on complete bikes, would you be better served upgrading components and wheels? A lighter set of wheels and a lighter bottom bracket/drive train might shed a few pounds and make your comfy bike soar up those hills.

I've ridden steel and I've ridden aluminum. I like my steel. But you can get a harsh ride with steel and a smooth ride with aluminum....it all depends on how it is crafted.