I like your car choice, wagons are nice mix between people and cargo and MPG
Mod tips (links are to our wiki mod page for that mod):
1. grill block is a cheep easy first mod.
Grill block partial or full - EcoModder
2. smooth wheel covers
Smooth wheel covers - EcoModder
3. belly pan
Belly pan - EcoModder
4. Rear wheel skirts.
Rear wheel skirts - EcoModder
5. side mirror delete.
Side mirrors - EcoModder
6. Tire pressure to max sidewall.
Increase tire pressure to max sidewall - EcoModder
7. Scangauge
ScanGauge OBD-II computer - EcoModder
The first 7 are relatively cheep and easy to do. 8- 10 are harder but sill very doable.
8. Kill switch.
Engine kill switch - EcoModder
9. Kammback.
Partial Kammback - EcoModder
10. roof rack removal.
Roof rack - EcoModder
11 Full boat tail.
Full boat tail - EcoModder
this one is harder and will take some $$$ and time commitment. I just did it and it took me a strait week of work and about $300.
Issues with lowering:
1. will prematurely wear out your half shafts. I have a brother who tests them at work, keep the angle the same. Any change will kill them 2-3x faster.
2. reduces ability to go over debris in road
3. reduces ability to drive through snow (might or might not be an issue for you, I need 6-8" in the winter)
before lowering a car I would make a air dam to the same height and see if that scrapes or if it helps. It is also a cheaper way to get the same gain.
Front air dam - EcoModder
Is the car a gas or not?
Manual or not?
I hope this gives you some food for thought. I would also look through the other mods on our wiki, it will give you plenty to think about