I see that the Feds will give us up to $1,500 if we replace our old furnaces
with a high-efficiency furnace.

I've lived in my house for 20 years, and when I bought, the furnace was a
"few" years old. So I am guessing that it is at least 25 years old, and
probably about 65% or 75% efficiency.

Should I take advantage of this opportunity and upgrade?

I am thinking that one of these days, even though the furnace works fine, it
will crap out - probably in January.

I live in Maryland.