I'm thinking THD types of distortion.

Its interesting that you say about obscuring of details.. because that was kinda the thing that annoyed me. I could hear that there was a sound going on, but because it was too distorted I could not hear 'what it was doing' if that makes any sense.

Yes they do indeed distort more musically, but a solid-state amp that doesn't distort is even better in my view

If I could afford it, I'd have both.. all valve for jazz-ish stuff and active for the rest and studio use.