I think you answered part of your own question: That 5%
To address the other 95%
Public meta-data is cr*p.
Way too many tags (especially for readers that use the tags to create categories)
Manual, gives you a chance to Normalize the data before the final save.
Code:
Publisher Example:
Baen
Baen Books
Baen Books Pub.
Baen Pub.
Simon and Schuster (their distribution channel)
Junk, Trash, Cr*p

Same for Authors (with twists: for who is listed first, LN-FN vs Fn Ln issue)
To steal a line from Burger King (tm):
"Do it your way"