The books I have are in good condition, no loose, damaged or missing pages. Both front and back covers are undamaged, but the spines are creased from multiple readings, is that a concern? Other than the rule about no writing in books, can I post these?

As long as the spines are still intact (i.e. not cleaved), and they are otherwise postable, they should be fine. 

Per club rules, creased spines are OK but I've run into a lot of picky people.

I've had some older out of print books that I've sent.  For the more beat up ones, I select the latest mail by date and send a PM warning the person of the book's condition.  I'll state a date that they should contact me by if they do not want the book.  I make sure that it is clear that I will cancel the book so they do not lose their WL place.  But I've actually never had anyone ask to cancel on the rare books.  Folks seem thrilled to get them.  These books were all postable condition.  Just old and very well used.  I know I have much higher standards for a new book than I have for a 40 year old hard to find paperback.

But the warning does serve two purposes, they are warned to expect an older book.  And I have a record that they are aware of that.  

What Emily said.  In my limited experience, members tend to be more accepting regarding the condition of the older/out of print books.  But definately be upfront and pm if you have any concerns or reservations about the condition.  PBS guidelines clearly state that books with spine creases are postable, as long as the book otherwise meets postablility standards.

Just lately I've had a crop of books that I feel were too old and worn for posting, meaning that I won't re-post them.  But they were old and long out of print and I did want to read them, so they cost me a credit - no big deal.  If I'd had to buy them they'd have cost more than that.  So yes I'd say PM first and then no one will be disappointed, most people won't mind given the date of the books.

Cheers, Margaret 

I also tend to be more fogiving of condition if a book it out of print.  Especially if it's been on my WL for a long time. But I would still complain if it came falling apart or stained (yellowing is allowed).  But those sound postable to me.  (are any on my WL?)  As long as you can't see the spine through the pages.

I would take any copy of The Windflower by Laura London or Wildfire by Cheyenne McCray at this point.