[Fuzz]

Savings from a new furnace are going to be small. If you do get one, I'd recommend one with a multi speed brushless blower. This will allow you to circulate air better, with lower electrical costs, and improve comfort. As GoinAllTheWay said, though, best to make sure your ductwork is working properly first.

When we replaced ours, the big benefit was moving air more often, that kept the basement warmer, and the upstairs cooler in the summer. I didn't see much cost savings.