I remember being advised to go ahead with "duplicate" titles, if your new edition was
a. a different file format or upgraded file format version (prc to azw3)
b. improved version or "added value" (curly quotes, add italics, better proofing, add illustrations, add annotations / footnotes, add glossary, etc.)
Many of the older ebooks in the library are simply re-packaging of the Project Gutenberg "vanilla text" versions, and I don't think anyone would object to improved editions of those.
Particularly knowing the care you take to produce a classy book, I think you should go for the gusto!