Most of the time the main box is good enough. Fuses are still legal. There are a few boxes that are safety hazards, but if you have one you should replace it even if not planning any other work (some circuit breakers don't trip when overloaded!).
Hello, Federal Pioneer 15A Stab-Lok blue breakers (old style, without the holes) here. I can personally confirm their potential for not tripping when overloaded, along with the smouldering outcome...
Which means you have to fix the main box. Which is most expensive part to fix.