It's always best to try and save the original paint. Cleaning, polishing , touch up and wax go a long way. There are some cases that do require a full rebuild and paint.

Take this Super Mondia, some people concidered the paint in terrible shape and the bike in need of repaint. Not so.

These are before picrtures, frame dirty, paint oxidized, few paint chips here and there. The chrome in need of some TLC.