The only way you could reuse shots is if you have an high dynamic object like M42 etc.
Here is a sample of 5X5 Second RGB i took to check my filterwheel after i fixed it (stopped turning).
I used a stacked image with minimal processing, then i processed the original stacked image and processed it till i hit some noise.
After this i did blend the minimal processed image in the fully processed image and for a 25 Second shot i think it doesnt look bad.
First the stacked image without processing.
And second after the above processing (Quick and dirty job at that
).