With the 10% SP-back offer about to expire, as announced, I purchased another 10 booster packs today.
They didn't have any spectacular monster inside, but I managed to upgrade two monsters this way, and a few others are very close.
However my first objective is to get all my main summoners to at least level 4 (for starters). Baby steps... Still can't think like a champion or a diamond league player with no limits.