How big do the sparkling gouramis get? I think I read the dwarf gouramis get 2-3 inches?
Panda cories only grow to just over 1" and most other cories are small also (2" or so), not sure if the gouramis would be aggressive towards them or possibly eat them? I've never had gouramis.
IME cories are good bottom scavengers eating up all the extra food that falls there and have a low bioload themselves. I think what they clean up would offset what little mess they make rather well, so a few extras shouldn't add to your bioload enough to hurt. Besides, they are just adorable
My opinion anyway, maybe someone else can post thier opinion?