The Flourishes available have an 'upgrade progress' that never seems to go up. Despite having used the flourishes I've bought multiple times, they say 'Upgrade 0/10' in the shop. I assume that buying the 15 point version upgrades them completely, but why have a meter that says 0/10 if the only way to update them is with currency?
Go to the flourish shop and hover over a flourish you've bought. It says 0/10 upgrades, even after having used the flourish multiple times.