I'll agree with you about snails being present, eaten by fish and underutilized by fishermen... but dragonflies... might differ (based on my own experiences). I don't normally see those in early season stomach samples and when I am catching fish on those, usually it's about the same time I'm also catching fish on chronies.

Don't know why I don't see dragonfly nymphs early, maybe they're still hibernating in the bottom. Maybe they only come out when there's a food source for them and that early food source is emerging chronies.

Burke Lake is a good one for fishing large green dragonfly nymphs on the bottom.