I can't be of too much help, but my family briefly had an all-trac wagon a few years ago... and this is what I can tell you:
Yes, the all-trac can hurt the legendary 4AFE mileage, see:
http://www.fueleconomy.gov/feg/noframes/9136.shtml
The rust will be catching-up with the car by now, so inspect it VERY closely. Make sure that all of the standard drivetrain components are good, esp the center diff.
The engine and transmission should be no problem, they go forever...and it shouldn't be blowing smoke, either. Of course these all depend on how the car has been treated/driven (as always!).
All in all, they're excellent cars. The AWD drivetrain seems to be one of the most reliable ever produced (though Subaru has come lightyears), much better than the 4WD we had on our 1987 Tercel wagon.
Good luck!
P.S.: LONG LIVE BUBBLES!
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1990 5spd V6 Camry (Still kicking at 393,000km) 1991 Celica GTS -- Pappa needs a 3SGTE...and AWD for all this friggin' snow
Honda my A$$, you just can't kill a Yota...