I don't know if it really makes any difference or not, but I've heard that after an output transformer has about 20 years or so aging put on it, the iron laminations in the core have "aged" enough to cause what is generally considered better sound then it had new. That's the only thing I can think of that would make a vintage amp any better then the same amp built today.BTW, I've noticed the same harshness in the upper mids on my Scott amp. It's small, but there. It seems to be more noticable on some speakers then others. I've heard it is caused by the cera-caps that are used throughout the curcuitry. Replacing these with good poly caps should cure this. I have replaced just the output coupling caps and have noticed a small improvement. One of these days I'll get around to replacing the rest.
Dave