You can modify a gas engine too if you like to take advantage of alcohols better qualities. Alcohol isn't so good in low compression engines though.
Properly built, an alcohol engine gets better mileage and has tons more HP than any production gas engine.
There is absolutely no reason we can have high powered cars like the 60's/70's except running alcohol now that alcohol is much more readily available.
A diesel/ alcohol engine is freakin' awsome. Runs at 28:1 compression and produces gobs of power from a tiny little 4 cyl. Unfortunately NASA only makes them in conjunction with another company from Brazil for use in diesel electric buses they are building and using on an experimental development stage. Not available to us dumb Americans.
Nothing stopping Gm from making them though, except they'd be TOO efficient
PS. They are claiming 100 mpg service miles on these alcohol powered diesel/electric buses.