[David in San Antonio]

As with many Model A topics there are a range of opinions on the 6 vs 12 volt question.
Here’s how one newbie sees it: If there’s a fault in the 6 volt starter system and rather than fixing it I switch to a brand new 12 volt system with a new battery, fresh wires and a clear ground path, of course it will work better - but not because it’s 12 vs 6 volts. The 6 volt system works perfectly when maintained. If I do choose to switch to 12 volts I’ll want to do my research on the starter. I’ve read here that shoving twice the voltage through the original unit will certainly “pep it up” but also can throw the bendix gear into the flywheel hard enough to eventually damage it. As mentioned above, the horn will need attention, too. I’m not sure about the coil, the rest of the ignition system, and the ammeter.
Switching to a 12 volt negative ground system does allow you to wire in modern accessories. Some people here download apps to their phone and charge the phone right off the regular 6 volt system, no converter needed. This approach appeals to me for its simplicity but if you’re going to add air conditioning it requires 12 volts and there’s no app for A/C.

I am a big fan of LED lights. The difference in visibility and ability to be seen is enormous. Specifically, the focused LED headlights (not LED bulbs instead of incandescent ones) and LED panel (not bulbs) in the taillights. This is one example of technological progress that really is superior to the original Model A design. A side benefit is that they draw very little current, adding virtually no strain on the battery and generator. The ammeter barely moves when I switch on the lights. They are available for both 6 and 12 volt setups.