Thieving Hammer calmly put away the exposed wealth from Mirlo's bloodless corpse. Even though his free will had been taken away from him, he was still excited to steal so much.
He put the money into his storehouse, not inside his newly stolen divine ability. The Power of Wealth is not enhancing his power at all because he hasn't put any wealth into it yet. But he still didn't put any wealth into it because the Power of Wealth is temporary for him.
As a thief, he will lose the Power of Wealth divine ability once he steals another divine ability. If he loses the divine ability, odds are that he will lose all the wealth he put into it too.
So it is better not to invest in an ability that can be lost. Besides that, the greatest effect of the Stealing Abilities divine ability is not its potential to grant a thief up to 5 rank 9 divine abilities but its potential to rob an enemy of up to 5 of their most powerful divine abilities.
