Political power may not automatically follow great wealth, but it is hard to see how there could be power without it. The essentials of Count Waleran and Earl Robert's influence may have been their barons' loyalty and their closeness to the Crown, but without money that would have been denied them.

It would be very useful if we could know what their incomes were, but that is something we will never know. Of course we do know that they were very rich. Henry of Huntingdon believed their father to have been the wealthiest Anglo-Norman magnate of his day; Robert de Torigny had the same opinion of Waleran's position among the Norman magnates. Stephen of Rouen compared Waleran with Croesus, in a characteristic fit of Classical hyperbole. From these opinions we would be justified in believing that the twins' incomes were as ample as any other magnate of their time, and probably exceeded any rival but the king–duke if they were combined.

To try to be more specific is to invite inaccuracy. It is possible to juggle with figures derived from records of the royal and ducal government. From time to time the lands of the earls of Leicester and counts of Meulan came into royal hands, usually because of confiscation following on rebellion, and the royal officers paid their revenues into the English or Norman exchequers.