Mievo, you are going through a phase many of us went through when we first got our i-MiEVs: how to extend its range.
Air Tabs, vortex generators, wheel skirts, etc. are discussed in Aerodynamic Mods to Reduce Drag
Air Tabs, specifically: http://myimiev.com/forum/viewtopic.php?f=22&t=1396
You can read those threads and draw your own conclusions. I still haven't finished my partially-fiberglassed wheel skirts and haven't much motivation to do so…
Wheels and tires: even if you could find something that would fit and not cost you an arm and two legs, you'll be hard pressed to find anything with a lower LRR than the stock i-MiEV setup.
Weight - it doesn't much matter once the car is rolling. You could try removing a pound here and there, but it won't make much of a difference compared to the horrible aerodynamic losses at speed. For example, I now continuously carry a 50# box with two spare tires and a jack and lug wrench, in addition to the almost-50# trailer hitch. Even climbing hills doesn't matter much, because you recover a lot of energy when going back down the hill.
After five years with i-MiEVs, I simply say that my range is whatever I need it to be to get to my destination, and I drive accordingly. Having a dedicated GPS with a nice instrument screen (e.g., Garmin 255) gives a DTG which you can bounce against RR for peace of mind.http://myimiev.com/forum/viewtopic.php?f=5&t=566&p=32038#p25993
Most of the time I'm a leadfoot, but on rare occasions pull out my hypermiling tricks. Never have any worries, and still have never seen turtle.
My suggestion is for you to get some miles under your belt and develop a feel for the exact mileage to your verious destinations. Planning ahead soon becomes second-nature.