The "seafoam" I cant immediately see what it could do to this scenario. From their own data is appears to comprise of refined hydrocarbons (usually these in most of the addatives is napthalene) plus isopropyl alcohol at approx 25% by volume of concentrate.
These are ordinarily used as degreasant etc and I can see that in pre burning fuel deposits they may have some effect. But that's not the concern with E fuels. It's more the fuel's stability in keeping it along with the water it may attract. Binding with oil may give advantage in this case, also the pressed oil is relatively safe to handle, carbon neutral and has the potential to coat the exhaust internal structure which may help with corrosion on some of these expensive systems.
I do feel that seafoam is just napthalene and isopropyl alcohol-ish in very small expensive bottles, which some would call snake oil I believe
Ethanol doesn't appear to give reduced octane rating (likely an improvement in certain proportions) and from engine internal components I've seen, burns with less carbon deposits that many of the proprietary additives claim to "clean" out of your engine.
As noted, it's not clear what these addatives can offer in relation to E fuels.
