I dont think it will make much of a difference. I played with a Variac in front of my amp for a while and it didnt seem to make a difference in tone at all. I am sure it was probably doing things with the internals, but nothing amazing happened. With the new OT though... the difference is WOW. It sounds like heaven.
The install was pretty easy. The clip on things for the new OT were too big, so I had to solder (spelling?) the wires to it, but it was super easy.