It depends on your expectations of finish quality and what you do to maintain it. Washes that have brushes that touch the paint can degrade it after one single wash. But do you personally notice it or care about it, that's a different animal.

Pristine is a strong word. To keep a finish pristine with less than moderate maintenance would require you to barely drive the car and keep it in the garage. You can do more damage to the finish in 60 minutes of highway use and a year of sun exposure than a couple machine washes will do.

Color makes a big difference. A white car can see a number of washes without a noticeable visual difference in finish quality whereas a black car will show tons of swirl marks with just one machine wash.

Finish maintenance is a big factor. If I run my car through a touch wash 4 times a month, but I polish it every 4 weeks, it will have a better looking finish than someone who only hand washes all year but polishes it only once every couple years.

And you have to come to terms with what your angle is. If it's maintaining value, it usually doesn't matter. A 6 or 8 year old car with a blah finish compared to one with a brilliant finish is barely a difference in resale value. Maybe a few more bucks to a private buyer. Otherwise book value is book value.

But maybe you enjoy a better looking finish and you find it personally worth it to keep it that way.

You're asking for discrete answers to your question but there are a large amount of variables that you haven't defined.

If you want to keep a darker colored car in honest pristine condition, want to use machine washes, and don't have the ability to maintain your finish at home, then you should expect to pay a detailer to polish and seal your car at least a few times a year.

Running the same car through a bunch of machine washes without maintaining the finish will quickly result in a poor finish.

But you have to define your definitions of pristine and poor, and why it's important to you.