I'd like that midfield with Sneijder/VDV - Sissoko - Marchisio, but we shouldn't expect too much from either of those 2 when it comes to their defending duties. I rate both players higher than D'Ago when it comes to skill, but I'd have to say I've only seen a couple of D'Ago games, where I watch our national team play all the time and also used to check on Madrid regularly to see how the Dutch are doing. It all depends on what kind of player you'd want.
Most people see D'Ago as the perfect type of player, to play really deep in the middle.. not sure how they'd do in that position. If you stick them on the left/right of that 3-man midfield and Momo in the center, it could work out pretty well.
Drenthe I'm not too sure about. I've seen almost every match in the U21 Championship and yes: he was pretty impressive. I had also seen him play for Feyenoord in the Dutch league where he failed to impress, and I don't think anybody needs explanation of how he did at Madrid.. I wouldn't take that gamble.