I guess that was my question: Why?
I don't have much concern running E-10 fuel in my car. If any rubber bits rot out, I'll replace with Viton or a modern replacement. As for the ethanol absorbing moisture, I add Sta-Bil Marine in the fall and fill up the tank fully. Corrosion risk throughout the system - sure - but I can get gasoline without the ethanol if I try hard enough. Usually not worth the effort.
As for the valve seats, if hardened valve seats haven't been installed by now, they probably should be. It is not a big deal for a competent machine shop. But, nevertheless, it will probably take many, many miles before the head actually suffers sufficient valve regression from unleaded fuel (E-10 fuel is unleaded) to require new valve seats. You are more likely to suffer valve regression from running too lean, thereby causing excessive heat at the exhaust valves with consequent valve regression from too much heat (also known as burnt valves). For a couple of hundred dollars you can buy some exhaust gas temperature gauges with which to monitor exhaust gas temperatures (which interpolates to leanness). Essentially that is what O2 sensors do on modern cars. I have them in my race car, but to be quite honest, the temperatures are almost too low to be recorded at low speeds most of the time. Of course, I'm more interested in the full speed at wide open throttle readings.
Just my internet opinion.
