Furnaces made these days are jet propulsion style burner, so there is rarely any real cleaning involved except for maybe spider webs or dust that gets sucked into the burners occasionally.

In terms of efficiency: It depends on climate and how much you actually use that furnace as to whether it's worth the efficiency gain.

Because 80% and lower efficiency use metal flue pipe, so to convert that to PVC can be quite the challenge not to mention costly in addition to the higher cost of the furnace. So if you live in a more moderate climate you will never recoup the cost.

To get the efficiency up there's additional parts, additional heat exchanger. In addition to all that you need a condensate line run because it will generate waste water. That adds to maintenance costs that you won't have with an 80% furnace.

If the job isn't retro fitted well, the higher efficient furnace won't work. It will spit out error codes like a bad robot.

That said some areas may require you to upgrade to the more efficient furnace. Location, Location, Location. (The 3 L's of HVAC)