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. I have followed some brands like ARC, VAC, CJ, and Cary, occasionally auditioning. My feeling is that the evolution of solid state has been faster that tube (coming from further behind). But tube amps have evolved towards better resolution very substantially… while digital had to get more natural.
Give that, I would expect that a restored twenty year old tube amp will sound good… but not perform at todays standards. If it were me, I would compare using your amps as a trade in, as is, versus using your upgraded amps as trade in. Perhaps that analysis would help. I actually traded in my 15 year old Pass x350 at only a reduced value of $500.. so, the trade I got was only $500 less than I paid for it… helping offset the cost of my new amp substantially.
I am retired. I did a major upgrade a couple years ago. I am so happy I did. I spend over three hours a day listening and being awed by my system. It was worth it for me. But you have to look at your own situation.