Is there any value in self-publishing a book as an academic?
I would recommend that you ask yourself a question: why do I want this book "officially" published?  You could, after all, just make the material free online via arXiv or as a webpage or an archival technical report of various types depending on its contents and your situation.


Prestige of having a published book?  A pay-to-publish press will generally give you negative credibility, since there are so many publishers that will publish your book without making you pay (including lots of dodgy low-quality ones that will publish pretty much anything).  Pay-to-publish smells like desperation or resume-padding.
Money from sales/royalties?  If they thought it was going to make money, they would be paying you, not the other way around.
Higher visibility?  A pay-to-publish press will generally not be any good at promoting your work.  They're not going to invest any real money in promotion if they aren't expecting to make significant money from sales.


Serious and reputable academic publishing houses are always looking for good books to publish.  The right ones for your field will generally have booths at the major conferences in the field, with representatives that you can talk to.