I would be more supportive of the program if it actually gave you cash for your clunker (instead of a rebate on a new car). Then people who wanted to give up their car and bike (or take transit) could do so. Or how about $4500 in bike and bike repair vouchers. That could last you for years.
My wife owns a reasonably fuel efficient vehicle, so we can't do a trade in even if we wanted to. That'll teach her to be responsible.