So the snail won the drag race...

Well,a multi spark ign may or may not improve the gas mileage.I did make a home made water fogger system and installed it in my Grand Caravan,it used windshield washer fluid. Mileage did improve by about 10% .Synthetic fluids in everything would help some too,even wheel bearings.My good friend here has built several hydrogen generator/boosters for many of his cars.He has made the local paper several times. This absolutely works in a non computerised vehicle,not only will your mileage improve dramatically,but you will see a noticeable power improvement and also a huge drop in emmisions..A computer programmed vehicle will see a lean condition and dump in more fuel to compensate,doesn't work.
Heres a good example of a working booster.

http://www.free-energy-info.com/Smack.pdf

It's easy to make,and I based my more simple water fogger on it.