Not that I can afford to buy them yet since I still have upgrades to buy, but once the upgrades are done, basically wondering if it's better to do stage 5 for tons of gold medals or a different stage (like 3) where it's easier to get platinum medals. --- Generic Signature.
You only get 1 platinum medal for every 500 gold medals you cash in. It's not worth doing it until you fully upgrade Juliet, buy every combo, and get the Love Nick achievement. Just be sure to save a good bit of gold in case you need to buy lollipops during a playthrough of Hard/Very Hard Mode.