To get the engine working efficiently and loaded up on torque, you need as much cylinder pressure as possible. This means small duration cam to keep the sweet spot low and as much compression as your local gas supply will allow.

Yes, going to E-85 will cost you in mileage as it takes 30% more alcohol to make the same power as gasoline, so your burning more of it. But, total cost involved may also be a factor. In my flex fuel vehicle, 04 Suburban, it is a wash cost wise when gas is $2.95 and E-85 is $2.35. If the price spread gets greater than that, then E-85 becomes more economical from a financial stand point. Below that price point gas is better.

I also agree that you don't want to spin the engine to low. To cruise down the highway only takes 50-60 horsepower. So you want to have the maximum amount of torque at the smallest possible throttle opening regardless of rpm, within reason. This will be much more efficient than spinning the engine slower just to keep the rpm down.

Everything that applies to performance engine building applies to mileage engine building. It is just that the return is greatly diminished. Sure, roller cams may provide less friction across the rpm range and at peak power are worth an extra 12 lb ft and 10 hp. That same set up in a mileage build may still have reduced friction and increased power, but only have an extra 2 lb ft and 2 hp. Also, total cost involved is a determinate of what you want to do. You could easily spend $20k building a trick motor that will only get 3-5 more mpg that a good solid blueprinted and balanced build up that costs $7-8 grand.

For the car, you want to lighten it as much as possible. An A body is already kind of small, so you punching a much smaller hole in the air than a E body. Not much you can do for aero as a dart is a brick no matter how you look at it. Skinny high pressure tires, synthetic grease and fluids to reduce resistance, a whole bunch of little tricks can gain you a lot.