[Creeper]

Lowering the car is a personal choice if you can live with the limited ride height and harsher ride its all good. If your only opting for the springs and not willing to get a full setup it might not be worth it. As for the CAI in the winter a warm air intake might help but raising air temps might hinder that. Colder air is denser and allows for better burning of fuel. If your not on the gas hard it will help. Not all performance mods decrease fuel economy. If you get the CAI I'd sugest a AEM filter as they are dry flow and all you need is soap and water to clean them. If you get a CAI try and get a more free flowing exhaust again when your not hammering the car it will help. Look at your engine as an air pump. The better easier it can breath in and the better it can breath out the better your economy will be.

If you want to lower your rolling resistance you might want to look at 13"-14" light weight narrow rims. Short term gains may not seem that great but long term will be. The benefit of a metro is that 13's would fit just fine. If you can get smaller tires as well you can reduce your rolling resistance.