Let's not think that Pirlo is the norm. Pirlo is a one in a lifetime player. His class is resemblent of the greatest of all time. Sneijder is just some mediocre dwarf who got lucky he had played under Mourinho with Eto'o & Milito or with Van Persie, Robben, etc...
Sneijder is not that good, he never has been. I'm not saying he couldn't do a job here but he can not lift this team in terms of quality. He simply can not. And that's why we're hesitating to offer him a longer contract.
Also that implies that any transfer sum we're paying is relatively seen much higher for the time we'll be ""enjoying"" his services. Everyhting says NO in this transfer. It makes no sense at all.