For the reason you just showed. That starting lineup would amount to nothing. To be an effective AM you need a great first touch, dribbling ability and vision. Sneijder has the latter but is somewhat lacking of the first two. Cassano has it all.
I don't agree with some of your points here Adam.
For example, Riquelme by some was great AM, but he had dribbling abbility worse than Gresko had.
Kaka(for me) is not a great "visionary" comparing to other great playmakers. For me he is nowhere near in this to Iniesta, Zidane etc. To me he has dribbling, spead, first touch, but not the latter.
What I'm heading too, is that there are different players playing that position, and all can be great, or bad. It depends on how the team is constructed. So playing Sneijder there can be both great/bad.
Now about your point that Sneijder should not play there, and you would like him better for the side midfield position, I agree with that, but not because of the reasons you stated. I would much better liked him at midfield, because I think with his workrate he can manage to play there in Serie A, and also give us a lot when it comes to technical abbility in midfield.
But I think he can play also in front of midfield if he has to, or on the wing. Hell, Dejan is weaker version of Sneijder, and he still played there, and did fairly well.
As for formaton, I would love if it would look somewhere like this:
-----------------Julio Cesar--------------------
-Maicon--Lucio/Chivu/Samuel---Javier/Santon---
----Sneijder-----Cambiasso----Thiago Motta---
-----Milito--<--->--Eto'o-------Cassano------