The "large" exp you see is NINJA exp, which only helps the 3 ninja you have with your main at the time to level up, if they are not capped (cap is the level of your main char)
As far as the important character exp goes, it's only 1500 per instance sweep, a really tiny value in the grand scheme of things. In higher levels, it's mostly negligible, thou I'm not sure how much impact it will have at lv 29.