It all depends. I have old stuff that absolutly would not be worth it. I have old stuff that gives up nothing to some of the newer other than a few ounces. And knowing how to do it and having all the tools makes more sense than if someone is starting on the bottom rung and asking...'can I do dis?'.... One of the best ones I ever did was on an late 70s early 80s possibly custom 531 frame with full high end campy on it. Found it literally brand new in mint condition at a thrift strore for $7.00 About a 60cm frame with a 56 TT. Exact size for someone I knew that needed a custom but couldn't afford it. Sold all the campy stuf off it for about $300. Rebuilt it with good nearly new stuff out of my junk boxes and gave it away.Rebuilt an older but really nice(like new) thrift store Bianchi with better stuff,from junk boxes, and sold it for less than my cost to someone that needed a deccent bike.And upgrading does not have to mean ultegra/chorus or better,like many seem to think.