Does an older house need to be rewired?

[Aleko Petkov]

I am rehabbing one apartment in a 1937 triplex in Los Angeles I just bought. Looks like the electricial wiring is original two cloth-insulated wires, although the kitchen and bathroom have three-prong GFI outlets. The main panel supplies 100amps for the whole building. The inspection didn't point out anything about the electricials, so I am trying to determine how much work is required vs what is nice to have. To rewire the whole building to modern codes and upgrade the power supply to 200amps would cost 15k. But what do I need to do? Can I get away with the existing wiring? I know new construction must be to code, but what about older buildings?