A good bump in tire pressure can cause your real world range to increase too. 44 psi is the side wall max. If you rely on the dealer to set the pressure for you many times they are set hot vs cold. To set a proper cold pressure you should do it first thing in the morning before the car is driven or before the sun is up. Just based on the way the dealerships do business this isn't practical. You drive the car in in the day get them hot then the tech drives the car. When a car is brand new the tech will usually take the car out for a road test before they bring it in the bay to see if anything sounds/feels off and hence the tires will be warm.
Also many dealerships have people that will set all tires to a standard psi for all cars, probably 33ish. The leaf recommends 38 (I think). When I got mine brand new the next day checked cold and they were 30 psi. So if you have your own pump (you can use the car one without the bottle of seal stuff) do it first thing in the morning. If you'd rather use a gas station pump do it close to home, pump it past 50 psi then first thing in the morning let air out till it's at the setting you want.
By the fact that you say "I routinely get 4.4 miles/kWh" I would assume you reset the gauge often. To really be sure you should reset it every trip. I'm not sure if you know but the one in the dash and the one on the energy screen in the radio are different so if you reset one the other doesn't get re set. If you don't reset it on every trip you take then it makes a manual calculation of your range difficult.
Also be aware that most commutes will have a drop/gain in altitude and a direction that is usually against the wind. For example my commute on the way to work I usually have the wind at my back and I live on the top of an escarpment so it's an easier drive. When I get to work and charge to 100% it will give me a GOM based on that drive, for a brand new battery they range in the summer 100-125 miles. However as soon as I start going back home I've got a harder drive so the GOM will drop miles much quicker. By the time I get home and I've gone 45 miles on 50%+ battery I charge up to 100% again and then the GOM based on the past hard drive will show 90-112 miles. I do a re set of the gauge every time I drive, in the summer going to work is easily around 6 mile/kWh at 55-62 mph mostly highway and coming home is 5-5.5. So when it reads high you are likely to turn around and be harder on it and when it reads low again you're likely to turn around and go easy on it.
As far as the spending $5500 to make your trip you can get a good set or light wheels and LRR tires for way less that will give you a good bump.
Right now tire rack has the kosei K1 TS for $129, 17 in 15 lbs each. You can get 16s as low as 12lbs, kosei k4r $159 (tire rack says 16s fit the leaf but centre caps don't so it's not listed, search by a 2009 civic to see it), 16in Enkei RPF1 which tire rack shows as a fit but doesn't come with centre caps, $211 13.7lbs or 15s but with the leaf big brakes only buy those at a place that can test fit. I have 15in SSR Comp that are 10.4lbs each for my winters, they JUST fit. Rota has a lot of cheap sub 13lb rims.
For tires you can use the Michelin energy a/s in any diameter, 205 60 16, 215 50 17 or 195 65 15 and that tire is regarded as being the best you can buy in North America.
http://www.tirerack.com/wheels/Whee...se&filterNew=All&filterWeight=All&sort=Weight
