I tried this before, but the topic tends to be met with ignorance or apathy. In the end, YES, playfields absolutely do cure and harden over time, but the question is, how long and how much of a difference does it make?
If you talk to any CC guy, be it playfields or cars, every one of them readily admits to a necessary curing time, and that time is measured in either weeks or months
Stern is mum on the topic.
CPR's instructions are to let one of their playfields sit for 45 days or so.
High end playfield restorations with glossy smooth thick clearcoats take weeks in-between coats to cure and polish, ending in months of effort.
As for me, I sat on my XM LE for a few extra weeks due to timing, vacation, etc, and it was a good excuse to "let it cure." I've seen other XM with significantly more dimpling than mine, but who's to say the other one doesn't have significantly more games on it?
I had a CPR space shuttle playfield that cured over 6 months and wound up lifting inserts as the wood dried out and the CC hardened. I have another that cured perfectly, has extra layers of clear coat, and many months later the CC is still softer than playfields that are years older.
So the question is what is your own tolerance? Perhaps, a few years of playing results in so many dimples it just looks like an orange-peel clear coat (i.e., you can't identify dimples any longer). Perhaps letting a playfield cure for weeks/months/years allows the playfield to retain most of its shiny smoothness even after many hundreds of games.
The most relevant test I can think of is to find someone who bought a 2 year old NIB Stern and compare it to a game that was routed right out off the factory floor than sat, and at the point when both have the same number of plays, compare the playfields.
http://pinside.com/pinball/forum/topic/how-to-treat-a-new-playfield