Yeah, that's been my experience, too. Power tubes aren't really going to change all that much. Sure, there is a noticeable difference, but not drastic like changing speakers, or pickups, or, arguably, preamp tubes.
FWIW, mine had been modified to use KT88s, too, but I preferred EL34-types better in my Uber. That's been true for my Marshalls that originally had 6550s (very similar to KT88s), too. I do like KT88s in my 20th Shiva and in the Twin Jets I've heard (but don't own yet).
Anyway, all that's just my opinion. Different stuff works for different people, so yes, absolutely, have fun with the hunt!!