Sounds like you should just follow your own advice and put the thing on craigslist and get your money back. You're unhappy with th design, you're unhappy with the mileage, you're unhappy with the power, you have a tough time working on it, etc...sounds like you're just plain unhappy with this truck.
As for the mileage thing, let's jump in our mental time machine and go back to the mid nineties for a sec. Gas was around a buck a gallon back then, manufacturers were not obsessed with stretching the mpg's as far as they could. Ever driven a comparable mid-ninties SUV? Jeeps - worse gas mileage, Ford Explorer - similar mileage, Mitsubuishi Montero - similar if not worse, Pathfinder - similar, Isuzu - similar, noticing a trend? Hell, my 94 Ford Rager 4cyl got the same mileage that my 94 runner 3.0 does now.
These things are old SUVs, what does everyone expect? If you want good mileage than fork out the dough for a newer SUV, buy an older CR-V, or get a civic or corolla. Seriously.
I do not think these 4runners are the be all end all for perfect SUVs. The perfect SUV, or car for that matter, doesn't exist. But these things are great, dependable, and long lasting workhosre trucks.
As for working on it, find a Toyota Field Service Manual and make at least that part of your ownership more pleasant.