I'm gonna have to kick you in the NADS CrMo! You've already got the 'Creme-de-la-Creme' of (Japanese) mass-produced Vintage tourers in your stable and you're STILL not happy? Are you suffering from 'The Grass is Greener' because of frame-build location?
About the ONLY thing better than what you already have is a limited-production niche-builder or a full-on custom-built frame! And No, I'm NOT talking those heavy clunkers mass-produced today. Yes, those 'special builders' bikes come up every so often on the used market, but you've gotta be quick!
Or what about a late '70s P-15 'Touring Paramount'?
https://bikehistory.org/catalogs/1977.html https://bikehistory.org/catalogs/1978.html Looks like the 77s were the last of the chrome socks era... Note that even those were 26 pounds!!! On second thought -- your Miyatas are probably 'better' bikes!!!