As long as the frame and body aren't rusted through it is worth restoring, especially with you willing to do the work yourself. Given what the mechanic said, I would guess he doesn't have a clue to the value of clean 1st-3rd gen Toyota's, is a Jeep/domestic guy, or was hoping you would ask if he wanted to buy it.
When clean, the 1st-3rd gen('79-'95) Toyota trucks(both 2 & 4 wheel) hold their values rather well compared to their domestic counterparts, even against the Tacoma, and with U.S. market automakers no longer making a mini-truck, their value should only increase in the years to come.
