... I figure all the lights are 12 volt anyway so why not simplify the system and make everything 12 volt.
FWIW,I made my house system 24 volts, kept the bus system at 24 volts. I'm very pleased with the way it has all worked out. I would say if you have to replace it all anyway because its bad or dangereous, have at it, but if it works, why fix it. It sounded like your main fear is needing a jump start and not being able to get it. If you have a 24 volt house system you're all set and can jump yourself.And with a 24 volt system, if you need to jump start your truck, boy will that sucker spin! (just don'e have anything else turned on or you will fry it)