I'd go with the impeller every other year too, but for peace of mind...
1/ Lube grease nipple points as the grease does dry out
2/ Clean fuel filter on the side of the engine
3/ Remove thermostat, use a copper wire brush and lightly clean it (use new gasket)
4/ Remove propeller, grease prop shaft and use new split pin
5/ Clean electrical bullet connectors
6/ Check battery strength and top up with distilled water and put on trickle charge
Rather than upset the carbs (been there, done it), drain them at the drain screw, and check for contaminants, etc. If they're clean, leave 'em!