How many chickens do you have?
Daily scooping up their poop and generally keeping the run/yard dry can help to reduce smell, flies and parasites.
As I don't use Spinosad I don't have own experiences to share, sorry. :confused:
I don't live in the U.S., but I never ever would spray my whole premises with it as it is very toxic for aquatic organisms and such.
There is no need to kill every living insect to make it 'safe' for your chicken, on the contrary, chicken love to eat insects, even flies.