The most wealthy Outfit members were the ones who invested their dirty cash in profitable legitimate businesses such as clubs, real estate, oil firms, food companies, car companies, music companies, garbage etc. These guys usually didnt want the top spot and remained as crew bosses or high profile associates. As crew boss Ross Prio was the guy that you can take as an example or Hyman Larner and Eddie Vogel as high profile associates. These guys almost had the same power as their bosses. According to some reports, when Vogel retired from the oranization he had over 20 mil stashed "under his bed" plus real estate

As for Accardo, yeah during his prime time he was maybe one of the most richest mobsters in Chicago but i dont belive that he had much money left when he died. The problem was that he was a very well known crime figure, almost like Al Capone, so it was very hard for him to use other people as fronts for his legitimate enterprises. Many people were scared. He coudnt operate from the shadows even if he wanted to. He elude the law very well but you can imagine the ammounts of cash that he spent just to acheive that.