If money is constrained I would highly recommend yo listen to Schiit.That's the problem. The Schiit is plentiful. We need upgrades! :)
I have to applaud the music loving OP and a couple of other posters for getting a system you love and just...*loving it* for 20 & 30 years. It screams 'mentally stable'.
I know I'm not alone when I say there have been about a dozen amps in my life during that span. And PREAMPS. Christ, I can't even remember more than a handful of 'em.
Another option for the OP, if you love your stuff that much, perhaps you might think about 'modding' your pieces with some, if not all, of the caps replaced. Look at it like preventive maintenance, and it is. Old is magnificent, but caps do dry out.
So you can try out a Schiit Bitfrost MB directly from Schiit. If you don't hear a moving difference, bounce it back. They take returns.
And the mods, you can spend anywhere from a couple of hundred to a serious $600 or so. Depends on who, what, where.