Super Scroll Method:
Just like your weapons, your equipment may also use Maple Administrator's Gift Box which guarantees you stats with each upgrade. It will grant you +9 of your class' main stat and consume spell traces as well. The reason why this works so efficiently is because end game your %stats scale much harder than pure attack/magic attack. So having a total of 10 slots would grant you +90 of each stat which is going to scale extremely well. Apparently Nexon's stat ratios have been skewed since % potentials were released, so there's no exact scaling from stat:attack.