Here is Spartania Casual Strategy treasures for quick reference. Since Spartania released their treasures, there is more incentive to enter arena and attack someone successfully. The treasures upgrade your hero, entire squadron, defence hp and attack by increments of 5% per level i.e. 2 levels of the treasure upgrade is equivalent to 1 upgrade. I find it more efficient as it upgrades entire squadron of same troops, buildings and defence structures instead of 1 unit at a time. At high levels, the number of treasures needed increases about like 1, 3 or 4, 7, 12, 20...
