hey man, if you want more milege per gallon out of ur crx, there are 3 basic things you can do without getting into a lot of science.
One is of course weight reduction. Since ur car is already only 2000 pounds, i dunno if going any further will benefit because it will be dangerous to be driving such a light car going that slow. This might not be a problem if you only drive 65 on the highways (which i'm guessing you drive that slow because your getting such good milege already). So if thats not a problem, shedding some extra weight WILL help you even tho it is not very noticable. you can shed a lot of weight with a CF hood and lightweight rims.
2. aerodynamics. areodynamics believe it or not actually help a lot. it is not only for top speed. even tho you might go so damn slow on the highways to get good milege, it still is a crap load of drag. maybe you can find areodynamic front and rear bumpers. getting just those two parts will help on highway milege. oh and. if you happen to have big ass dents and random holes where air can leak into ur car, those will affect areodynamics.
3. efficiency. comparing the energy going into ur engine and comming out, the energy comming out is ONLY around 20% of the total energy going in (ie, gas, spark, etc.). you can remove AC, improve engine parts to lessen friction and also improve them so they will not steal as much energy. remember the engine and the whole drivetrain is the problem here. at every point along the drivetrain energy is lost due to sound, vibrations, heat, etc.
now about FI. since i'm not too sure about this topic, this is all i can tell you. if you go FI, yes you use more gas. but using that extra gas means more torque/hp at a certain rpm which means you can rev lower on the highway. now does that extra gas equal out the lower rev ? i dunno. theres the question for you. (this is assuming your turbo is small and it spools low) if you have a big turbo that isn't really spinning the right way when ur on the highway, then it just adds that little restriction to ur intake cause its spinnign backwards or not moving.