In my line of business, there are guys who literally work for nothing. I let them do it. I charge people a fair price considering my time and cost. Some think I'm high, others think I'm cheap.
Inevitable, yes. Now what the timeframe is varies according to different factors. I've seen pics of show cars stored in climate controlled storage with paint failure.
I've never really seen any filling ability with Z5. It does darken the paint slightly and I prefer the look to Z2. it's still a good product. Wolfgang is nice if you want to try something different.
I was at the track a few years ago. There was a guy with a 65 or 66 Mustang. I looked and it was a K Code. The guy pulled the original engine and was enjoying the car.