I've learned there are 2 kinds of bike parts , the consumables such as chains, tires, brake pads, and chain rings and rear sprockets as examples that can wear out, sometimes quickly, and more permanent parts such as frames, forks, seat posts and stems, and to some extent cartridge bearing hubs, headsets and bottom brackets. My strategy has been to get the best I could from the second group and plan on replacing the first when needed. As far as frames go, Reynolds 531, Columbus, Truetemper, and Tange frames, butted and lugged, in good shape would be my preference, especially as older ones will often take nice 700c 35 mm tires easily. Nice chrome-moly 80s mtn bikes can be fairly light and very nice too. With these fine machines it can be bitchin to have several sets of wheels. I have interchangeable ones with studded snow tires and others with fat Slicks or gravel type tires, to suit whatever the day's riding requires. Since a quality used bike costs less, this paves the way for upgrades like cartridge bearings or extra wheels.