I don't know that the Prodromou example is necessarily a good one. The MP4-21 was designed by Adrian Newey. So, Promodrou's work either did little to assist Newey in the design, or it actually hampered Newey. (Or there's no way to give him either credit or blame.)
I'm not saying Ferrari should only go after guys at the elite level in terms of both proficiency and notoriety, though that would obviously be nice. I just don't see anything in Bigios' body of work that suggests his arrival at Ferrari, if it happens, should be greeted by a tickertape parade.
His stay at Ligier/Prost didn't really amount to much. His work at Minardi...well, you can't really hold that against him. But it does get sticky after that.
When he got to Williams, they stopped being competitive. When he got to Honda, they, too, stopped being competitive. And aside from the BGP 001, which apparently wasn't his, his work for Brawn/Mercedes hasn't set the world on fire, either.
It would be foolish to throw the blame for his teams' lack of success solely at his feet at the expense of everyone around him. Yet, it's quite obvious that his presence didn't help those teams recover at all, and that's what Ferrari needs right now.
I suppose time will tell the story better than anything else.