72 mph with the cruise in my 93 with synthetic oil i'm getting 29.7 on long trips. that's both the car telling me and my calculator telling me 29 mpg.
even with a heavy foot i NEVER average less that 24mpg city and highway combined.
i do enjoy "instant econ" and thrashing it, and watching it go below 2mpg.
Fuel filter is easier than plugs even IMO.
plugs will make a difference if yours are significantly warn that they are hurting mileage.