I currently run with a vbulletin database user that simply has all rights on all tables in the vbulletin schema. That is nice and predictable, but I would feel more comfortable if that user would have some restrictions.
Has any work been done to determine which grants are actually needed and which are not?
I've just removed the GRANT rights which shouldn't be there anyways. The most of the other operations are required, like ALTER specially when installing / uninstalling Addons or Updates.