If you don't mind taking a risk and actually succeed Genesis 20, your damage will increase a lot more than if you were to invest in equips with the mesos. Though, I'd try to resist gambling and build my equips first. Once you can 2hit Skeles, there really isn't any point in buying Genesis skillbooks unless you're going for 1hit, which requires a ton of effort to do. You also have the benefit of using the equips you buy to gain more MP to HP wash on another character.
