Yeah, just install on top of 2.6.3. Well, i haven't done this for a long time. If anything, you can just uninstall and do a clean install (leaving the profile in place). It won't fix the already corrupted history files though, but at least i don't see corruptions in new profiles.
Why.. because there is currently no maintainer\lead developer for Spark. It is pretty stable and has some new features and fixes comparing to 2.6.3. But there is also some issues like voice chat (patch is in the work, but not sure how long it will take for cstux to complete it), it should probably also be upgraded to the newest Smack before official release, but that needs lots of work and testing. If you ask me, i would release it in the current state