At 84k miles & 21 years old, your plug wires will rot before the plugs 'wear' out. The plugs /might/ go downhill from fouling if you drive frequent, very short trips. I doubt any mileage gains will have any chance of a payback at this time.
That said, 'good maintenance practice' says you are nearly due for Plugs/wires/coolant exchange/maybe ATF service.
I wouldn't sweat it or hurry, but if I were going to be making a long drive, I'd probably plan to do it ahead of time.