the cars in overall don't break up as fast and that's nothing to do with requiring ethanol. it's just that they're better. or rather they made really really shitty cars in the '80s.
and what happens? well the farmers don't have gasoline to fuel their fucking tractors, that's what. which is quite the point.. the ethanol economy as it is in usa is dependent on the oil economy - it cannot hedge against it! all it does is _WASTE_ more oil.
there's plenty of alternative ways to fuel the cars apart from using ethanol. if it's a hedge at least require them to grow the ethanol using wood-gas tractors or some crazy shit like that(crazy as it makes no ecological sense to do it now, nor ever, not until we run out of coal to turn into diesel).
as it is, the tech is proven if you want. so it's not a hedge against anything right now to pay people to make ethanol out of corn. note that there are other ways to get ethanol in some quantities, from wood scraps etc, that do make sense in the way that the biomass would otherwise go to waste. but using corn for it and dictating a minimum amount to use is nothing but a corn subsidy.
(oh and if you were worried about adhering to global co2 contracts about dictating biofuel use, then using the wood scraps gets you double the points. but I really doubt USA gives a shit about that)