Seed production in Japanese maples tends to be rather variable, with some years producing an abundance and other years hardly any. Spring weather can have a lot to do with it - mild, warm springs with no late frosts tend to encourage seed production. And because of the tree's focus on seed production, leaf development may be less, resulting in a sparser canopy.

Heavy seed production can also be an indication of a tree under stress so that is something to be on the look out for. Weather in many parts of the country was a bit off normal this season with excessive warm weather and even droughts and that could certainly be a contributing factor to the lack of fall color and early leaf drop. Just make sure you are providing your maple with adequate water and other necessary cultural requirements and it should be fine.