20 Year Old Amplifiers compared to 2017

My take is that this one of the most informative threads on AG in a while with very thoughtful responses. I recently got an First Watt F5 amp, my first Class A amp, and it is a glimpse into music that I had never heard before.  I dunno if all pure Class A amps have similar performance to the F5, but it is the pinnacle of amps I have had over 45 years.  It is not as powerful as my McCormack DNA .05 amp, a Class A/B amp, but between the two of them, I am very happy.  I would be very keen to find an upgraded Krell KSA-250... it is the one Class amp for which I lust. 

I am a denier of the SQ benefits of Class D amps, but I have not heard the best of them. The ones I did hear seemed to be bereft of the total musical involvement I enjoy with Class A and Class A/B amps.   I am a lover of vintage gear myself.  Again, this a great and informative thread. 

Kosst,
My F5 at the moment is being worked on very capable DIY'er, who, based discussions he has had with Nelson Pass, is doing some the upgrades you describe above.  It difficult to imagine the F5 improving, but it is logical thatat it will do so with the improvements you describe.  
Finally, there are lots of facts and opinions stated in the realm of audio blogs, but yours I consistently find the most logical and informed.  Thanks for sharing your information.  Whitestix