FWIW, I took the air dam off my '05 and there was a noticeable hit to efficiency. That actually kinda surprised me, because I didn't think it would have enough impact to be detectible by itself. It was, and I ended up putting it back on.
I like the active air dam on the '21, you save the fuel without it hanging down there when it's not needed.
I like the active air dam on the '21, you save the fuel without it hanging down there when it's not needed.