I think 35 year old amps with replaced capacitors, etc can be every bit as good as "modern" gear, but I do think a move to tubes would be an improvement, even if your amps were 2 years old. That being said, if you want to keep the simplicity of SS, I think the Luxman that Clio9 recommends would be very good indeed.
Amplifier progression and change
I have Harbeth SHL-5s with vintage Accuphase P-300/C-200 amps. It's a nice combination, but I'm thinking of updating the amplifier with a smaller newer integrated, but is it that easy? My question is this: will new amps from companies such as Blue Circle, Plinius, Luxman, LFD, Accuphase, etc. clearly blow away 35 year old Accuphase separates? Have enough advances been made that a new $2000 - $4000 integrated can best an old amp that was built nearly with a cost-no-object standard? Whether solid state or tube, what would one have to spend to get an amp that is head and shoulders above the P-300/C-200? Thanks!