Have the speakers ever been recapped? If not, start there. 20 year old caps are well past their sell by date. Replace ALL with polypropylene or PTFE.
Going to a dealer is a waste of time as they do not have your speakers, cables, room or the rest of the system. You might hear differences, but they will likely not travel home.
If the speakers are ported, some tube amps may not mate well due to the impedance curve.
I’d add the VTA gear from Tubes4Hifi to the list....really excellent stuff that’s fairly affordable.
It's not really excellent stuff. See VTA M-125. People have all kinds of problems with them and have written after ZERO support from Tubes4FiHi. If you complain on their forum, they axe your account. A lot of their advice is just plain wrong!