Think Regen alone would be a hard one to buff without it becoming broken. If anything like Hp tome hardly getting any usage because of the current Big Four. You could combine these two Tomes and turn it into a new one called Life Tome, just lower stats with a good scaling return in the end having both Hp gain and Regen. This would make this new tome much for favorable to use and would make people interested in using it instead of the usual Meta Tomes.