[AeroModder]

Unfortunately I don't have the effects of every single mod I have on the car, because I haven't done much testing outside of just seeing how they affect daily commutes.

Currently, the aero mod list includes:
-Front air dam and undertray with a 1.5" splitter
-Kammback, sealed at the rear with small pieces of acrylic
-Side "rails" (not full side skirts, but a single strip of coroplast positioned on the inside of the tire running the length of the side)
-Front/rear tire spats
-Rear diffuser, with a 15 degree max slope
-Pressure Recovery Plates to help the diffuser work better
-Deletion: Mud guards
-Deletion: Passenger side mirror
-Driver's side mirror taken from a Geo Metro
-Hard corners added to trailing edges
-Smooth wheel covers

Engine/drivetrain:
-Cold air intake with drop-in K&N filter, custom tubing to pull air in from in front of the radiator
-Oil blend: 2 qts Mobil 1 high mileage full synthetic, 1 qt Royal Purple, 1/2 qt Lucas Oil Treatment
-Festiva transmission swap

Suspension:
-Civic VX wheels
-175/70/13 Hercules Tour 4.0 Plus tires, 45 PSI

Instrumentation:
-Sunpro Tach
-Scangauge II

As for what the mods have done, the biggest benefit from a single mod would have to have been inflating the tires. When I got the car, the tires were underinflated, and it returned a 38 MPG tank. Inflating them to 40 PSI got 43 MPG, along with me getting comfortable driving a stickshift.
The biggest benefit from aero mods would be the front air dam/undertray and the kammback. I found that vortex generators and a spoiler showed nearly the same improvement on highway MPG (38 stock, 42 VGs, 43 Kammback at 65 MPH with a mild crosswind).
Since your Aspire is a '94, a Scangauge won't work for you. That has proven to be an invaluable tool, and will be on any '96 and newer car I own in the future. Seeing the instant economy has really helped me squeeze as many miles as I can on the highway by backing off the throttle position ever so slightly. Ignoring it, I'll get maybe 45 MPG on the highway, but paying attention, I can see 50 on a steady cruise easy.

But I'll be honest, not all of my driving is focused on economy. I do enjoy sporty driving, and will on occasions start up quickly from a stop and stretch out the engine's muscles, so to speak, so that brings down my tank averages somewhat. As long as I know my mods are having a positive effect, I'm happy.