Theres nothing wrong with adding +2, but honestly Shin is just for the twilight drops and in my opinion this should be enough reward for fighting him. You get a kick-butt atma from him, completetion of abyssea storyline which provides 200k brews, and if you go after you've acquired the gear and atma then it's just to help others and costs 10k cruor to do so. Perhaps it's just too easy as it stands now and +2 shouldn't rain from the sky any more than it already does.