I agree it does no damage to the mechanical and valve portions of the
engine.

According to Marks Engr Handbook, the heating value of an equal mass of
10% ethanol gasahol is 96.1% of an equal mass of gasoline (I used
Hexane as an approximation to gasoline & assumed ethanol). Here in MN
the car mileage reduction is generally assumed to be about 5%. I see
that in the differences between Wisconsin gasoline vs Minnesota gasahol
in my vehicles.

Since the fuel mass flow in an aircraft carb isn't likely to change
significantly, and since the engine is a heat engine, with all other
things being equal, a power reduction is to be expected. Other items
such as compression ratio, timing, mixture proportions etc could be
varied to optimize the use of gasahol, but the heat value just isn't
there.

Who knows what the seals etc used in an aircraft are - except that
there are a lot of legal reasons that they are not being updated in
contrast to technical reasons why they should be updated. Actually a
simple aircraft engine has few seals as you know, and if the float
(let's see we're back to metal again aren't we) don't sink, and the tip
of the needle doesn't dissolve, we are back to mostly static seals in
the fuel selector etc. I don't know about fuel cell bladders, except
that given the regulatory climate, there is a good chance they have not
been updated for 50 years either.

I just had the seals go and the idle jet varnish over in my '87 Yamaha
M/C carb, and lawn mowers here routinely need carb work.

Vapor pressure is primarily determined by fuel temperature, although a
standard temperature is used for the Reid vapor pressure test. But
that standard temp has to be held very closely to make equivalent fuel
evaluations. In practical service the significance of the temperature
variation seems to never be addressed. For example, where is it
written that you can't paint your wings black? A chem prof once noted
that the vapor pressure typically doubles every 15 deg F.

I have to agree that only in a most marginal situation (probably
aggravated by the need for a fuel pump) might ethanol (b.p. = 172 deg
F) or especially methanol (b.p. = 148 deg F) put you over the edge into
trouble. My original response was hearsay.

The long term storage issue - the weed whip (manual) I just bought says
to throw away all ethanol laced gasoline after 60 days.

I agree booze keeps a lot better but that is primarily an alcohol/water
& flavor mix which does not seem to be subject to deterioration (maybe
shrinkage?) of alcohol hydroicarbon mixes.

Old sour gas is a problem here in MN. It seems to be aggravated by
higher fuel storage temperatures. My small-engine repairman neighbor
confirms this (as well as the rampant carb problems).