As posted earlier, charging systems output above battery voltage. They must do so, to get the energy to go "back" into the battery. Many racers using 16 volt batteries are not running alternators, so the max voltage the electrical systems see is 16 volts. They do make alternators that are designed for 16 v batteries, and they put out over 18 volts. This pushes the bounds for many electrical components.
Don't know much about the roundy round guys, but the drag racers are looking for the extra voltage to give them a bit more horsepower from the extra ignition output (easier starting is a bonus). The analog MSD boxes can handle the 16 volts, but don't like the higher voltage alternator output. In fact, cars without alternators must make sure the master switch is off when in the pits on the 16v charger between rounds, so as not to kill the MSD.
TurboStart sold step down boxes that would output small amperages of 12 volt power for misc accessories, but they are prone to failure. They also had batteries with a 3rd lug that one could get 12 volt power from.
Since pro touring is about so much more than just horsepower, and these types of cars tend to have a lot of electrical accessories, I would really cautious about 16v batteries in a street oriented car.

Correct, a properly functioning and designed 12V system is more than enough to run a standard and high demand car.

12v battery may not be enough to start
 

I see a distinct advantage to having more than 12V for starting. Aside from cranking, many ignition boxes need a full 12V to output anything.

When cranking, it is not uncommon for a battery's voltage to drop below 12V.
In this case you will have hard starting when using many popular ignition boxes. Newer computer controlled vehicles are even more sensitive to voltages below 12V.

What if you could run the starter/alternator, ignition, headlamps, fans and fuel pumps on the higher voltage and then regulate that down to 12V for the rest of the vehicle?

This should be easy, as most these devices should use relays because of their current demands. The relays could just source +16 rather than +12.

With a system like this the 12V should be rock steady at +12.6V or whatever you set it to, as there would be very little draw on the +12V side.

Am I missing something? Roy

I have used a East Coast Electric 16 volt alt and XS Power battery in my Mustang.Never burned out a bulb.Had a electric fan,water pump,msd and fuel pump.All the manufactures said it was ok.Charged at 19.1 volts

A properly-running factory or aftermarket alternator will pump out 14.5V- 14.8V, maybe even 15V.. so 16V for an alternator-less system isn't unrealistic at all. But running it in a dailydriver with a 16V-nominal alternator (as previously-mentioned, ~18V charging output) would be pushing things. From my experience when spec'ing various auto and non-auto electrical bits, things that are used in 12V applications have tech specs of "9V-16V source power" etc. I've yet to see anything 12V dc-intended that's rated up to 18V.