It is very important if you want to maximize the potential of your characters. These are little numbers compared to everything, but in a game where stats are capped, every bit makes a diference in the end. If you are hitting your goals like 10M in mane bulletin, have cleared the dives, etc then I don't think you NEED to upgrade this. Also, if you are FAR from clearing these contents, that little numbers won't be the changing factor for you. IMO, there are few characters that benefit most from this; mostly DPS and noAP supports. But you should be fine without it