[Flakbadger]

Welcome to the forums!
Just so you know, you don't have to get super fancy with a car to get better mileage. That is to say, driving technique has a lot to do with it. Aero mods are going to help you, sure, but a responsible eco driver in a stock car could probably surpass an irresponsible driver with an aeromodded car in MPGs.

It all depends on what you want out of your vehicle, what your price range is, and what your level of mechanical inclination is. I don't have the time or money to invest into something that needs TLC. I needed something dependable and economic, and so bought the Yaris. Older cars aren't going to have airbags, CD players with MP3 hookups or electric steering (no power steering pump). They also will need a lot of miscellaneous service and are more at risk for needing head gasket or other pain-in-the-*** repair.

Would I say "don't do the things on your laundry list?"
Absolutely not. I would just say, keep these things in mind. For example, I haven't had the time to start aeromodding yet and I'm still satisfied with my improvement in MPGs from my old vehicle.

Hydrogen is definitely exaggerated, by the way. I won't say that the members of this forum are perfect, but I highly doubt you will find a more realistic bunch. If you read up on it in this forum, you'll probably come to realize that seeing a "20% improvement in MPGs" is utter horse****.

Anyway, good luck and again, welcome!

EDIT: As for vehicle suggestions, everyone is in love with the Metro on here, and I can't say it's a bad vehicle for MPGs, but I personally don't trust them in crashes. Anything Toyota or Honda is going to treat you right, and if you get a Honda Civic from the 90s with Lean Burn, you are going to be hitting 40 MPG without much effort.