Dragonflies eat other insects, not plants so you don't have to worry about them. I've never seen a caterpillar eating Vinca or Hibiscus here, and there's no damage to leaves. But I do have a lot of other plants that the butterflies like. If they're just visiting the flowers, they are nectaring, not eating the plant's leaves.
Never see butterflies on any of my plumeria either. Funny, you'd think such a fragrant plant would attract them.
