Experienced polishers charge around $100 per inch. Some charge less. The only ones i have had direct contact with are Robert Benson and Woody in Hawaii. (As a smith i polish my own work.)
Habaki on backwards,missing a piece, nakago beat to heck, blade doesn't look like anything special, mismatched parts, unlikely candidate for restoration.
Same covered saya may be an indication of a higher end sword, but not really an indication of when it was made. No pics of blade, so can't say anything...that handle is roached...if seller doesn't want to show the nakago, I would pass.
I suspect it has more to do with fitting koshirae than making it lighter or faster, as the amount of steel removed is minimal and would have little effect on handling.
Mune of nakago shaved down, anomalous scratches not oriented with file marks, freshness of mei .....could have been o-suriage based on height of mei to polished area and hint of hamon continuing past the machi. Interesting.
Some kinds of "wood glue" will accelerate rusting....ask me how i know.... rice glue was used and still is for good reason. I would avoid anything that would change the external finished surface, like wood glue.
My understanding is that Showato are always non-traditionally made swords; gendaito are modern traditionally made swords since the end of Shinshinto. Shinsakuto are newly made swords in the traditional manner, so perhaps there is overlap in the definition with gendaito.
Perhaps it is a language issue, but I suggest that in fact there are trace elements in the iron sands used for tamahagane, and in fact these trace elements end up incorporated in the end product, regardless of whether or not they have been placed into solution through reaching a melting point (they have not.) This has been well establish by a number of metallurgical studies published. I think we are revisiting this subject, and it has been covered here before.
I think we discussed this before, regarding Japanese smiths forging blades in the US and other countries....I seem to recall one of the names mentioned having a regular forge in the northwest US for a time.