Well as they say, it's the thought that counts. I doubt that anyone was thinking that one program was going to solve everything, but nothing is going to improve if no one does anything. So, environmentally speaking, it was hopefully at least a step in the right direction.
Only time will tell what sort of impact program(s) like that will have in the long term.
But that thought cost us $700,000,000,000 and got us nothing. What they should have done was buy clunkers from impound lots and dealer auctions for less. They could have taken a lot more vehicles and spent billions or less.