Dare, I think Force India went forwards (they gradually traded the "one day in the sun" ability for the chance to be consistently reasonable everywhere) but with Fisi on board they would have got there faster. Tonio was a bit of an all-round disappointment and it was sometimes difficult seeing him in the Force India knowing Giancarlo could have done better. Adrian was quick but the technical side is a bit of a weak point for him, so having Giancarlo there to help with technical direction would have been a big plus.
That said, given that di Resta would have resulted in one of the two Force India drivers being removed in 2011. Given that Adrian seemed to be unusually popular within the team, I would not like to have bet that Fisi would have kept his seat in 2011. And Ferrari were not likely to ask twice...
There are teams out there that would be better off having Fisi in the car than at least one of their current line-up (Renault and Williams definitely and maybe - dare I say it? - Mercedes and Ferrari). The trouble is that by the time the teams had realised their collective mistakes, Fisi was effectively off the table - Renault, Williams and Mercedes know they can't prise him from Ferrari and Ferrari is having more trouble locating decent sportscar drivers than single-seater ones...