Every night there is a new build of zenphoto made with the days patches. These builds generally are stable, but they have not had the extensive testing that happens before a release. So, you use one at your discression. If you choose to do so, download it from http://www.zenphoto.org/files/nightly/ and install it just as you did the released version.
If you wish to try spamassassin, give the nightly a try. The worst is that you revert to what you were running previously. Let us know how it goes, specially your use of spamassassin. From the nature of the bug that was fixed, I am pretty sure no one is using it in this release!