Good move, HT is a wasteland of bad sound. Stereo integrated tube amps are the sweet spot of high end audio. Its what I've used for about 30 years now, and that was after extensive comparisons including some time with a McCormack DNA, one of the better SS amps around. Don't even consider receivers, vintage or otherwise. Or if you do consider them then at least take the time to hear one head to head against an integrated. That will be the end of your consideration period. And good riddance.
50 watts in a tube integrated is plenty, especially with your speakers. The thing about tube amps, everyone focuses on the tubes when really its the transformers, circuit, caps and connections that make all the difference. Go listen to two different amps that both use the same tubes and you will see instantly what I mean. Yes its true KT88s do sound different (a little more silky and 3D) than 6550s which sound different than the seductively smooth midrange of EL34s. But go and listen. You will see. You can't judge by tubes alone.
New vs vintage is harder. A lot of the appeal of vintage gear is, quite honestly, nostalgia. Which is fine. If that's what you're into. I mean that. Some of that old gear, nothing will ever look any better, and even then there's the undeniable appeal of that which has endured. What's new is new for a millisecond. What's good is good forever.
So you want to be selective. Especially with rebuilt. Anything gets rebuilt and you can forget whatever was before the rebuild. All that matters is the extent and quality of the parts and the skill of the rebuilder. Which could frankly be you.
That's one of the beautiful things about tube integrateds. Open one up, what you see is what you get. You could literally build one super killer amp all by yourself and knowing nothing simply by patiently replacing one part at a time. All you would keep are the transformers, chassis, and knobs. Everything else is point to point wiring. Caps have values printed right on them. Resistors, ditto. Diodes, all standard stuff.
If the thought of that turns you off then probably you should be looking at new, or rebuilt with a real good warranty. Because an old vintage tube amp is bound to have you doing that kind of thing anyway. Or paying someone else to do it.... eventually....
And oh, what you said about the build quality of vintage gear being unrivaled? Not even close. Remember: nostalgia. Take off the rose colored glasses, see the cheap screw terminals for what they are: cheap screw terminals! Amp designers just aren't the lazy profit mongers they're made out to be. Well not all of them anyway!