I'd suggest buying one ready to ride, getting some miles in, then deciding if it's worth the time, effort and money to renovate. fashions have changed, even on traditional steel tourers, most noticeably their stiffness. Whether you consider that a good or bad thing is a matter of preference, though that might be influenced by your size and weight. I love the aesthetic of skinny steel tubes, but the bikes I choose to ride are all OS tubing.
If I were going down this route, I think I'd leave the run of the mill bikes like the Dawes and Raleigh to one side. It's isn't that there's necessarily anything wrong with them, it's just that prices have dropped so low there's not much difference between them and something that originally cost twice the price.