On what basis Gilardino's more expensive than a younger Quag.
Fiorentina sold Gilardino for 8m eur in January 2012, when Gila was 29 years and 5 months old. Quag is right now 29 years and 7 months old. So, we can't really talk about a "younger Quag" in this case.
Gila was a regular starter and many times the leader and best player of his team. Player who scored more than Quag in 6 of the last 8 seasons. Player who scored 147 serie A goals and 18 goals in Europe (most in CL), compared to Quag's 60 serie A goals and 0 goals in CL. On top of this Quag recently suffered a bad injury and teams know that he's nothing more than a 5th choice striker in Juve, while Gila was a starter.
So back to my previous point: If Gila was worth 8m eur (according to Fiorentina), then Quag is worth at most 4 million.
In any case, Quag's price is certainly more than 4m eur, but my point is that Fiorentina surely won't value him at 8-10m eur, as proposed in one of the above posts.