I say if you will be using the car as a daily driver, go ahead and get the hardend seats. But if you are going to put limited miles on the motor anyway, just leave the iron seats alone. You shouldn't have any problems with erosion if you only drive the car ocassionally.
After all, the heads can only stay original once, and if they do wear out in the future you can just get them changed then with a valve-job.
I think they still sell "lead additive" that is supposed to replace the lubricating quality in fuel. If you're worried you could mix that with the gas.