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!
This is not an answer to your question but I had Super HL-5's for about 6 weeks and the best sound I ever heard from them was using a Vac Avatar Super.
I do not think they make an integrated but check out Bel Canto's eVo series. They ae magic. And BTW different technology from that of 35 years ago and other of today's SS amps for that matter.
I'm guessing the Accuphase is a solid state amp, and if that's the case, a modern solid state amp will offer sonic advantages over what you have. A relatively inexpensive amp that I can recommend is the W4S ST500 with WBT outputs. They also make an integrated STI 500. If you are ennamored with Accuphase, check out some of their new models.
If it is a tube unit, you may not find a significant improvement.
I don't want to burst your bubble but I owned those Accuphase amps over 35 years ago. At that time they were made by Kenwood and sold at circuit city type chains. They were nice but not state of the art. With the speakers you now have you should invest in better electronics; there are many out there in your price range.