The date on the furnace says 1993. So far I have replaced the pressure sensor switch and now the small electric blower motor inside the cover is making noise which indicates to me it will need to be replaced soon.

The question: Given these issues, the age of the unit and the ongoing concern of energy efficiency, is it time to think about getting a replacement furnace?

15 years is a good amount of time for a Goodman unit and many others. There are other parts that can cause problems the older it gets.

I would let your wallet decide the issue. If you can afford new go for it.