Kk, I'd like someone to confirm this, but I believe I have the bonuses to plunder(not ally bonus, plunder) that def pots give. The bonus is 1/2 the cost of the def pot. So, for example... The weakest def pot ($1,250) gives you an extra $625 to plunder should you win. If they run all 10 pots, you will recieve an extra $2742500 to your plunder.
Oh, so in comparison to the equal powered atk pots, the plunder bonus is 1/8, or 12.5% of the atk pot of equal power's cost.