About 40% of the time, I lean towards the thoughts of keeping it. Any other person I talk to who owns one, or knows someone who has owned and sold, says the biggest regret was selling it. In my ideal world, I keep the NA1, AND get the NC1. However, it is hard enough to justify with my wife why a good chunk of the garage is taken up by a car that doesn't get driven all that often..... plus, the proceeds of the sale would be what funds the new one. It is more the realization that any work done on it (which has been extremely minimal, thanks to the legendary reliability of 90s Honda) is going to be harder and harder to do as the car gets older, parts get harder to obtain, etc... Your exact line about a museum piece, I have thought to myself as well. Do I become a caretaker of an antqiue, or sell it to collector who makes it number 6 in their collection that will properly preserve it.
I had the front repainted this summer (clear coat was peeling after 31 years) and a few of the shops around town that specialize in exotics (Maranellos for instance) wouldn't do it, because they said if they broke a clip taking the bumper off, the replacement ones are no longer available. Sort of was the catalyst for a lot of these thoughts. Horton Autobody did the work, and did a fantastic job on it. But still, was the first time I had a shop turn away the work because of the "difficulty" of workign on the car.
