When I bought my boat, I figured after 40+ years that I'd need to gut the entire system and start over.
After looking things over, I decided against it. The factory original 12v system is still neatly wired, and not spliced or hacked into.
No, the wire isn't tinned but it isn't corroded anywhere either. The insulation is stiff, but not cracked or failing anywhere.
The color coding isn't up to modern ABYC standards, but I believe ABYC makes allowances for older boats. Basically, you just stick with what you have, or you totally upgrade to the modern color code.
The only part of the 12v system that's messed up, is where PO's added extra circuits. They were tied to empty slots on the bus bars which is how the original system remained intact. The additional wires were/are sloppily run, spliced with multiple colors of wire, wire nuts used, that sort of thing. I've been sorting that out as I find it. You just wouldn't believe how the auto bilge pump was wired. I've run out of extra slots on the bus bars so I'm adding another because I don't want to splice or piggy backing circuits.
The OEM 12v fuse/switch panel has run out of slots so I'll be upgrading that to a new, larger Blue Sea Systems panel. Blue Sea is pricey but I like all the little niceties that they come with, like a mounting template and LED back-lit labels.
There was no 120v system, which made things easier. I needed shore power because I was going to be living aboard.
I'm no Maine Sail, but I did my best to comply with ABYC standards and cable everything neatly to avoid strain and chafe. My only regret is that I didn't know about the SmartPlug at the time, so I still have the old 30 amp twist-lock style cord. I went with a Blue Sea AC panel and installed 3 GFCI outlets, each on their own breaker and an onboard Guest 3-bank battery charger.
Later on, I added a 750w standalone inverter. It's not tied to the boat's 120v system, it has its own outlets and a USB port. I stick the iPad/chartplotter to the bulkhead and plug it into the inverter via the USB port. The inverter really only gets used to run small power tools, electronic devices or a shop vac when shore power isn't available. I'm not trying to run a microwave or water heater or anything.
The great thing about LED lighting aside from the extended battery life, is the low load that they put on electrical wiring. That increases the safety factor, IMO.