Spamming cure I has very little strain on your MP pool. You should try to save Cure II for when you have a proc of Freecure or if a party members health drops by over 1000. If no healing is required, you can save the Freecure proc for up to 15 seconds. This means you can wait those 15 seconds while your mp regenerates, then cure with cure II as needed for no cost!

For those pesky moments of AoE damage on the party, you may want to use Medica 2 as although the initial heal is low, the regen is provides is quite potent. Using this in conjunction with divine seal is a fine party heal, and any subsequent AoE healing needed after the initial Medica 2 can be dealt with with Medica I.