Superpose different image areas seperately
Sometimes, different areas of the input sequence needs different settings to get better results. (E.g. another input range) Just create more Superpose nodes, change the settings which matches the best for the specific areas and compose them to a final image.
Stabilize the sequence before superposing
Superpose only works on stabilized/fixed camera images at the moment. When not using a fixed camera, stabilize the sequence, superpose it and attach the movement again.
Retouch footage with snow or rain in foreground
After superposing a snowy footage, you can subtract the original image from the superposed image to extract the snow/rain layer. After retouching you can add the snow again. You can also use the difference matte effect to extract the moving objects.
Lesser input frames can cause better results
If you have a lot of objects moving on the same path (e.g. a highway), too many input samples can cause a worse result, since the objects are covering the same area again and again. Begin with a small number of input pictures and increase step by step and watch the result. Also try to vary the “Every n-th Frame” parameter.