Wow, I never knew there were Smart Roadsters, they're very good-looking little cars.
I think the first order of business would be to find out if the "fastback" from the other smart roadster will fit on to your car.
That would take care of a lot of your problem right there. The "Del-Sol" type rear roofline isn't doing you any favors right now.
Other than that, those rear wheels (mainly the wheel wells) look like they could use some help. They're very "flared-out" looking in the pictures. I think they could benefit a lot from some wheel skirts.
Oh, and welcome to the forum!
