Hardly anyone pays for first class, but will they pay three to four times as much to arrive a few hours earlier?
(On a personal level I hope there isn't a market of even more people who want to come here who'll be enabled by greatly shorter flight times. We had more than enough tourists already, TYVM. But economically, we won't be able to resist because jobs)
I think you might underestimate how many people would visit if the long-haul flights weren't an obstacle. Pre-covid Iceland, easily reachable from Europe and the NE US, had over 1M arrivals on a population of only 300k: https://en.wikipedia.org/wiki/Tourism_in_Iceland
But I think you must be right. If the trip becomes less burdensome more people will want to come. The obvious (to me) response is to set a target tourist number, and raise the arrival fee until we get approximately that number of tourists. But now we're getting into policy :)