A repaint hurts. A vintage bike with good original paint original decals even with scratches and fading and a litle worn decals is more valuable than a repaint.

A dent hurts. Ex: A very nice Masi 3V last year sold for less than $600. It was a mint original paint job, decals were perfect, all Campy SR - but it had a dent about 1/2" in top tube from handlebar impact.

Lower-end equipment hurts. Campy NR or SR on a vintage road bike is desired. If it has other equipment it's less collectible. The higher-end only works, though, if it's period correct. And - if the bikes were sold as complete bikes then the equipment must be correct per the catalog. In such cases lower end equipment will help the value if that's what it was originally equipped with. If you see Campy NR brakes on a Raleigh that came originally with Universals, then you would want to replace the Campys with Universals.

Columbus SL or SLX tubing or Reynolds 531 tubing is the high-end steel you want to look for.

Lugged steel vintage bikes are more desirable than welded steel vintage bikes, although I'm not sure how many vintage welded frames there are.