Do 3 star rankings unlock anything in Luigi's Mansion: Dark Moon?

Solution 1:

According to https://gamingreinvented.com/nintendoarticles/luigis-mansion-dark-moon-three-star-ranks/

The Reward for getting Three Stars

For getting three stars in all missions, you get another E Gadd medal on the file select screen and next to your name online. In case you were wondering, the first one is gained from beating the final battle and the last is for filling up the Vault entirely (including all ScareScraper specific bosses).

Additional source: https://gamefaqs.gamespot.com/3ds/632930-luigis-mansion-dark-moon/answers/352042-three-star-rating-importance