>This has been debated to death on guitar forums, but some would argue that digital is now undistinguishable from the tubes.

I find that it's impossible for the average listener to identify the difference in recorded music, especially if there's a lot of distortion in play, but I can entertain the idea that it's a detectable difference.

As someone who moved from solid-state and digital amps to tube amps I find there to be a huge difference in terms of dynamics and response, which massively influences the way I and others play. I can't imagine Jeff Beck or Gary Moore getting the same results with non-tube amps, since their playing relies so much on dynamics and physically feeling and moving air in the room.

edit: for live touring, though, it's so much more efficient to use digital or solid-state options for size, weight and reliability, if it doesn't directly impact the artist's ability to perform

I have never used a top line modelling amp, like kemper or whatever...but I immediately play better through my tube amps than lower end digitals (Katana or whatever). It is dynamics as you say. Anyone would prefer to hear me play (as if) through a valve amp (vacuum tubes are called valves in Britain). Valve amps are still the default option for higher end enthusiast amps, although modeling is taking over with pros for convenience

As compute power continues to improve, so does simulation.

Yeah, I would expect modern software able to do the job for all but extreme cases. Basically, custom Amp mods.