We have come to appreciate the creature comforts, the safety and the performance of new cars. It is so tempting to "improve" the ride for what ever seems to be the annoying features of the 90 year old technology. From reading many things and viewing old advertising videos of the time, it seems apparent that the clunky, noisy, bumpy cars were very much the current technology back then. The Model A lasted 4 production years and went through numerous (quite numerous) changes during its run. It seems that the "New Ford" was itself a trial run even as the first ones were being produced. So, Henry & Co. was improving the car as faults were discovered. Keeping and restoring the Model A to bone stock condition is a pursuit that competition contestants do strive for. For driving around in modern traffic, I think we do many "improvements" just so we don't feel like sitting ducks in traffic or so as to not crack it up. Things like turn signals and improving the brakes with cast iron drums. The list probably starts there. Alternators too. As has been voiced by many earlier in this thread, the word "improvements" is pretty darned subjective.
My own "improvements" include:
Cast iron drums
Basic floaters
Alternator (6-volt pos ground NuRex)
Battery shut-off and also fuse.
Nu-Rex base plate and points in distributor
Turn Signals + RH talil light
Thermostat
Inside temperature gauge
My car came with sealed beam headlights so I did go to Halogen
Modern shocks (My car had none when I bought it)
So, I've done several. It still runs and sounds like a Model A.
Some day I may go for a high compression head, balanced crank and even overdrive. My wife hates the uncomfortable seats. See how this thing progresses? Like a disease!
Oh, and what would Henry approve?? None of it. He wanted to stay with the Model T and didn't much approve of the A to begin with. Ha ha.