I am planning to use my macbook for casual gaming and mostly school work. Do you think it is worth the extra money for just a casual gamer? Most games I play are on 800*600 and the lowest so I don't really mind graphics. I just want 30+ fps.
Assuming we are talking non-retina, the main upgrade you get between the 13" and 15" models (besides the larger screen size obviously) is the dedicated graphics card, a good one at that. You say you are only a casual gamer and dont play very demanding games. If that's the case then the 13" will suit your needs very well. But if you were every interested in playing any more demanding games then the dedicated graphics card would be a must if you wanted to keep fps high.