Try to buy one built between about 1960 and 1975. 1960 is when drywall pretty much took over from plaster and 1975 is when the baby boomers all started buying homes, and in some places they lowered the building standards (and allowed aluminum wiring instead of copper, spruce floor joists instead of fir and particle board underlayment instead of fir) to allow cheaper construction so that they could provide less expensive homes.
1. Copper wiring
2. Copper plumbing
3. Fiberglass insulation
4. Plywood subfloor
5. Plywood underlayment
6. Cast iron vent stack for quieter flushing
7. If there's a finished basement, finished garage or deck, ask who did the work. (Cuz if the previous homeowner finished the basement, the garage and built a deck, he's going to be wanting the same increase in value as if it were built by a builder, and everybody knows that you make more mistakes the first time you do anything than the 50th time you do it.) Quite simply, his labour on a first attempt shouldn't be worth the same as experienced labour.