I have a 93 GEO tracker 2 door, 5sp 4x4, 30s. It gets 26-30mpg. The gears are swapped from an auto for the 30s. Its 1.6 FI.
Great for moving around town, and really surprised how well it does on trails. BUT, I live in Phoenix AZ, and if I want to travel to Payson or Flagstaff, forget it. The hills make the drive undesirable (at least for me). If you do not mind less than 45mph then you would be OK. You would need to stick with near stock size tires and/or swap gears for larger tires.
I would think any sub compact with larger tires that has around 110hp and 80 hp torque will suffer in this area.
I'd highly recommend anybody looking into this find the same vehicle you are looking for with the same mods and take it for a drive. If possible, look for gradual climbing hills and see how it does. You may be surprise.
If I were to turn my Tracker into a mini expedition rig, I would install a Tacoma 2.7 motor (double Hp and Tq). If your looking at a subcompact with and larger tires in mind and for see your excursions in hilly area, you may want to research for possible engine swaps (MPG in mind).
Not trying to bash subcompacts, I keep watching for a 2.7 in CL, so one day I may have one myself. (I like less with more, and the turning radius great!)
Ryan