When is a frame worth repairing? that is a very good question! I have recently completed and full restoration of a 1964 Flying Scot that tbh if I had found it on eBay or the likes I would have written it off as beyond economical repair! But it was my Fathers old race bike so scrapping was not an option. I replaced the steering tube so I could use the original forks, but to be done properly it needs a new seat tube, bottom Bracket and the rear dropouts replaced. I restored it as best I could without the major frame work and it looks pretty hanging on my office wall but it does not ride like it did in 1964 lol.

But where do you stop with frame repairs? You soon get in to the 'Triggers Broom' scenario (link if you were not into British 80's sitcoms lol) https://youtu.be/HisD_pqlRHQ

Its like finding Eddy Merckx's last Tour winning bike but having to replace every tube and drop out..Would it be his bike? No I don't think so. I think to sum up If a bike has historical or sentimental importance then its a very grey area. If it just to make a fantastic bike great again then its a £/$ question on what you have.