Lens flares are on our list of things to add.
(Dynamic) ambient occlusion is a nice technique, but it only makes sense in scenes with high geometric complexity (read: lots of surfaces intersecting at acute angles, such as indoor environments, foliage, buildings etc). While we can simulate a lot of interacting objects, a typical scene in Universe Sandbox² rarely meets those conditions, thus the benefits of AO would most often go unnoticed and incur a performance hit too large to justify the minor visual improvements.
For complex objects (like space stations, hint, hint) ambient occlusion will be baked into the object textures, which is not as fancy as a dynamic calculation but looks just as nice for our purposes.
Keep the suggestions coming,
George