Errol, normally the answer to hardened exhaust valve seats with unleaded is no you don't need them unless the engine will be put under heavy load for long periods of time. Based on what you are saying of your needs, you will definitely benefit from this extra machine work and exspense. I just got some head work done from a very knowledgeable engine builder on my stovebolt. He asked if the engine is going into a motor home or was going to pull heavy equipment going up over the pass, I said no, end of discussion. If I were you, to keep the valves in the head, I'd do it.

1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY Gallery
Video of the 261 running

1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration