I have published an academic monograph in Spanish based on my dissertation with a university press in Spain. I have reworked the book since then and translated it into English, would it be dishonest to try to get it published in English (I would of course mention that the book originally appeared in Spanish)?
It almost certainly depends on the contract you signed with the publisher of the Spanish version. Many book contracts have a clause that stipulates that the publisher retains the right to license translations -- in other words, it may be that you don't have the right to publish the translation without the consent of the publisher, even if you did the translation yourself.
The prudent course therefore is to read your contract for the Spanish version again, and if in doubt contact the publisher.