A ruffled band is a great way to add length to a mini dress because you can make your ruffle up to 12-15 inches long. Treating a dress this way will enhance the casual vibe of either a peasant dress or relaxed mini dress. The secret is keeping the amount of ruffling in check so the gathers don't make your ruffle balloon out in an alarming way. No one wants wants that.
My dress was 44 inches around at the bottom. I cut the fabric so when I sewed the bands together, they'd equal 110 inches which gave me plenty of fullness for gathers.