"My experience over the last forty years of owning top level amps… although in the past mostly solid state (but my preamps and phono stages have been tubed) is that, ten years is a significant improvement in performance… and twenty is in a completely different league.". --. ghdprentice.
I would be the other dissenter then because my experience is the same as yours. Even really great equipment 10 or 20 years out has been surpassed, even in the amp category. I also tried to upgrade a top of the line tube amp and preamp 20 years old, 15 years old by having them be rebuilt and upgraded with the latest and the greatest parts. Unfortunately I ended up selling them and buying newer high-end amps and preamps.
Now the upgraded equipment was much better than the original and there were obvious sonic improvements but just not as good as the latest and greatest equipment.
Even the very idea people on this form are saying you should upgrade and tweak the equipment you've got to modern day standards should tell you that modern day equipment will be better. Of course modern day equipment at the equivalent purchase price of the old equipment.