I just got some vague sense that by buying it he'd become spectacularly wealthy, like, top 1% wealthy (although he already put down 700 million dollars with seemingly little issue... How much more rich could he really get?). You're right though, it's never explained why or how, we're just meant to accept that it will. It's too bad we'll never know how much ended up on the cutting room floor and what sort of movie we might of had if it hadn't.
But in lieu of an actual answer, I think Toad's is as good as it gets. Is Altobello supposed to be like a Luciano or Bonanno or something? How good of a job do you think the GF trilogy portrays italian mob families from those various periods?