Are there plants that would help attract more dragonflies to my yard, or is it all about the water?
Dragonflies are predator insects, but thankfully they are not interested in people, only other insects. They feed on aquatic insects when they are developing underwater, and they feed on mosquitos after they have emerged from the water and spread their wings. From what I have read, dragonflies need clean water, so, anything that can be done to maintain the quality of the water in your local streams would be helpful in increasing the dragonfly population. I suppose that you could try and breed mosquitos as dragonfly food, or maybe it would be better to avoid spraying for mosquitos, and just let nature take its course.
Dragonflies and Damselflies do like areas with clean water. They also like to rest on isolated tall plants to hunt their prey/protect their territories. We have horsetails and cattails, (contained, due to their invasive nature), that the male Dragonflies love. We also have a juniper with a dead branch at the top that the hummingbirds and Dragonflies fight over. Surprisingly, sometimes the Dragonflies win. Since you live in Minnesota, I doubt you have to worry about an insect food source for them; should be plenty of mosquitos, mayflies and gnats available...