A 1000W generator is not going to make much of a difference in range.
Here is the aero/HP results for your car:
http://ecomodder.com/forum/tool-aero...ToStep=5-200-5
=5.07HP/3870 watts @ 40 MPH, not counting efficiency losses.
You would need at least that in city driving to extend your range significantly. I believe that's one of the reasons that Ben removed the generator from his Electro-Metro in the end.