Recently bougt a 4K monitor to play Flight Sim 2020 on. Going from a standard 28" 'HD' monitor where I thought the graphics of MSFS was incredible to going to a 4k 28" is just out of this world!
I think eventually, they could be worth it. That is, once 4K144hz monitors become more common. For now though, I think 1080 240 or 1440 144 is the way to go, assuming you have the means to get high frames at those resolutions.