Things that could be done faster (in order of importance):

* Use some partitioning scheme to make collision detection be
  less than O(N^2).

* Implement cropping of individual sprite frames to save memory. RLE
  accel already takes care of this to a degree.

* Sprites that are just for display (ie effects) does not need
  masks or all of the features of regular sprites. Make them a
  separate type of object.

* Change alarms from O(nr waiting) to O(nr active) (ie to a sorted queue).