I agree, yes, yes, and yes! In addition to smaller leaves, I think you need more branches and more "branchy" branches, for the lack of a better word. This is a cool stylized tree, so I wouldn't want you to ruin it by adding too much. One easier thing to try as well would be just make the trunk twice as long before any branches, and maybe add a knot hole or two. You may also consider straightening the trunk a bit, just because large trees simply don't grow very high if they're this crooked. They'd just fall over. The trick with trees is that the size is almost directly proportional to their age, so making it look older could make it look bigger in some ways.
@EAlexanderis right that your camera lens can play a big role. Also consider where the ground plane would be that a photographer would be standing, and put your camera there (lower).