Hi. I dont need metal tracks for my Sherman. They are pretty robust and I dont think I will need to replace them for decades. (But running over concrete is like sinking the tracks in acid...)
But the king tiger is a complete diferent story. The tracks are poorly designed, the pins are open and are conected just with a couple of plastic milímeters at each side of the track. A lot of people breaks the tamiya king tiger tracks at the first run.

So far I have only run my King Tiger inside home, but Im sure the first time I run it in the garden over grass or mud I will break the tracks.

But ausf you are right about what happens with the upgrades... I know that If I install metal tracks on my King tiger, I will need to replace the track tensioner, adding a gearbox brace and maybe bearings in the shafts... And then I might have another kind of problems, lol.

So it seems you can never reach the perfection... Im not sure what to do, but I dont want to have a shelf queen acumilating dust for years.