Here's what the Book Condition Guidelines say about the book's cover:

Cover:

• Must both be present (front and back)
  • note that a paperback missing its front cover is  usually an illegal, unsold copy
  • "cover" does not = dust jacket.  Hardcovers do not need to include their dust jackets to be swapped here.
• Cover not water damaged (there may be no water damage to any part of the book)
• Cover not torn or chewed/gnawed
  • some used book stores cut out a small part of the cover; if the amount missing is less than 1 inch, this is OKAY
  • a small rip (less than 1 inch) in the cover is OKAY
  • yes, that does say "chewed/gnawed" above.  That means no pet-chewed (or human-chewed) books.
• A bookplate inside the cover or on the flyleaf is OKAY

A creased cover is okay, even a small rip would be fine.

I would accept the book. I don't think we are supposed to worry about overall value. People shouldn't be looking for books for resale vale... OR should I say... expecting books that are resellable or valuable.

I know I have found some wonderful rare books here... BUT I want them for me... so who care if they look *used* LOLOLOL

I think excessive wear is a good way to look at if a book is postable and would you want to receive i

I think as long as it's not folded up like an accordion it should be fine.  If it was creased in several spots and looked mangled then I would say it falls into the excessively worn catergory. But yours sounds postable. When the book gets requested: just turn down any RCS that say something like "I only want books in like new condition" or something similar.  Personally I turn those down anyway even if my book looks brand new.  Most likely you won't get one of those RCS anyway.  But you never know.

I've posted books with a creased cover before and didn't have a problem. 

Creases on the cover don't interfere with the story, so I wouldn't have a problem receiving it.

I wouldn't have a problem with it either :)

I don't mind a creased cover :)