NSFW is awesome.
First, your poor jeep. My cherokee(98) before I put stupid lights (parachutes that light up really) on the roof and a lift I got consistent 22-23 mpg, my best of 24 in one 20 gal tank. (5 speed/6 cyl, no roof rack). Now with all the stupid stuff I did to it I get 17-21 mpg. Put a stick in it, tune up and some aero mods, you already have it? And its a tough wagon?
Neon. I would love one but they rust beyond use up here. Make mine with the 2.0 DOHC or do a stratus 2.4 transplant w/low ratio gears for low revs on highway.Bolt on srt4 turbo stuff later if your just getting too good gas mileage.
Saturn. Well there not quite what they used to be. We have a L300 WAGON! It has the Evil (but oh I love it) 3.0 DOHC v6. Has 4 wheel disks and 4 wheel independent suspension. Rides nice, is quickish and ugly enough to be cool. The engine is beautiful but apparently not the most reliable. I have yet to Ax this but want to sometime. Gets about 26mpg.Traction control gives this thing an edge in the snow. You have to love this engine to own one, they need love.
Focus, this would be my pick. They have become cheap and there is a strong aftermarket now. I want one with rally suspension and big mud-flaps. When we got the saturn wagon we drove it side by side with a focus wagon. Focus was in a different class (economy car) and saturn was nicer. Looking back the Focus wagon was smarter B/C of efficient 4 cyl and actually being reliable (well some of them anyways) Plus a rally focus wagon would be sweet.