First- Congratulations! The Miyata 1000 is a "lifetime bike." This is a 1985 model- it's a pretty slick model. It's a triple butted frame with Deore XT and 600/Ultegra components- from back when Deore XT was the top of the line. So basically it was a top of the line frame with top of the line and 2nd from top of the line components. It was pretty close to a flagship model bike. IMO- a bike of this caliber is as capable as any modern tourer, while being much more elegant and graceful.
https://www.ragandbone.ca/PDFs/Miyat...logue%2085.pdf
This would have come with 700c wheels with a 5 speed rear end. My guess is it was probably spaced around 126. Just a guess- but you'd probably be able to get a 130 in there without much trouble- so yes- you could go to 10 speed with this frame- I'm running a 10 speed 130 hub on a 1985 frame. However, this bike is equipped with friction bar end shifters- these shifter do not have the fine tuning ability to accurately shift between the cogs on a 10 speed spaced cog.
This is a "grail" level touring bike. It's a "touring bike." It's not a "go fast" bike. Touring bikes generally have brakes that are more robust than "racing" style bikes. They're meant to stop a bike, a rider and a rider's touring load. This bike has Shimano XT cantilever brakes- among the very best brakes ever made. If you were to switch to Ultegra side pull brakes- it probably wouldn't have the stopping power of properly set up cantilevers. Additionally, you'd have the unused cantilever bosses sticking out of the fork and stays- and that would look stupid. Not only would it look stupid, but it would also broadcast that the owner was stupid enough to not use cantilever brakes.
While I believe people may underestimate the handling of touring frames as heavy and slow- I think you should also realize these bikes were meant to haul heavy loads over great distances. They were not built to be lightweight, "quick" handling, or particularly nimble. This may not be the ideal bike to have a powermeter on. You may like the Bio
Pace rings, you may not, or you may not notice the difference.
IMO/IME- this is a bike to have wide tires on (in excess of 32mm- more like 35 or so).
This is a bike that was meant to have around a 26 pound fighting weight. If you're expecting this bike to handle and respond like a 21 pound racing bike- you may be disappointed.
You have a full-on touring bike with a full compliment of custom sized racks that were designed and fitted to this bike. To remove them kind of neuters what this bike is about. The rear racks look to be custom fitted to this size frame with the rack bosses in that particular location.
You also may wish to remove and set aside the Miyata Radial tires- of if you're into parting out your stuff- the Miyata Radial tires are pretty unique and could possibly bring some decent money.
People that are into "modern" bikes don't often understand how awesome the Mirrycle mirror for non-aero levers actually are. They look really old fashioned- but they ALWAYS point directly behind you- regardless of which way your head is turned- and it's just a quick flick of your eyes- you don't need to look for and locate the mirror, then think of where the mirror is pointing.. you glance at the mirror and you know where it's pointing and immediately see what's behind you.
You have a REALLY REALLY desirable bike- based on your questions and comments- it seems that this bike may not be particularly good fit for you. I would urge you to evaluate what that bike was created to do- vs. what you expect that bike to do. There's a good chance you could meet in the middle- but I would also not try to fit the square peg into the round hole.
best!