I don't think you'll see it with the frequency people think. Giovinco was an exception to the rule. The other players that came from Serie A were usually older and were looking for that one big payday. I don't see the faucet opening any time soon, especially with the younger players.
His contract with Roma runs out next year, but with the way he's been playing this year and if Roma miss the CL (and with the way they've been playing lately it's a very good possibility), they will need some money. I could see them jettisoning his contract, especially since he's the highest guy on the payroll.
I'm not sure where they would fit in it though? You going to put Lampard or Mix out wide? DDR usually anchors in front of the defense.
I don't see MLS gaining ground on Serie A anytime soon in terms of football. In terms of stadia, it's already passed it, but Serie A has finally woken up and knows what it needs to do. Juve's got its great stadium, Udinese will have their renovated soon, Roma's breaks ground this year, Milan could break ground this year or next year. Fiorentina will have a new one soon as well. Teams are finally waking up and realizing that they're missing the boat with the status quo.