fyi,
wikipedia lists the 2011 leaf as having a cd of 0.28 with an area of 7.80 sq ft (3,401 lbs). CDA 2.184
For comparison it lists a 2004 prius as a cd of 0.26 and an area of 6.24 sq ft (2,890 lbs). CDA 1.6224 (~%75 of the leaf).
So there isn't a whole lot you can do about the weight or frontal area on the leaf short of a new body, rolling resistance is going to be a bit more of a factor, and the cd isn't too shabby, but aerocivic level mods (CD of 0.17) could extend higher speed range by maybe 60%, probably more like %50 with the increased RR.