Upgrading a piece of equipment would increase the level requirement of it for 10 levels. For example, he decided to upgrade his beginner deck that didn't have level requirements. Once he upgraded it, its level requirements would increase by 10, to be level 10. So he only upgraded it 3 times to level 30, so Ace could use it.
Another thing that should be taken into consideration was, the grade and the type of an item. They were also became deciding factors on how many stats it would. The monster cores that were used to upgrade the item also decided how much and what stats that would be increased.
After knowing the stats difference between the beginner deck that had been upgraded 3 times and the four elements deck that was originally a level 30, Ace considered his new deck as heavy rain that had ended his drought. Although it was not a special weapon, its value was several times higher than the master thief's cloak. Furthermore, it was an S-grade weapon.
