I think he'd be as good a signing as Moutinho in the long-run. Considering he'd be half the cost now (less?!), has a couple of extra years on his side and won't arrive with all the weight of being a former club captain, International regular and supposed 'next big thing'.
Portugal & Holland have to be two of the best countries in terms of producing a steady flow of top class players, so both have had a good footballing education thus far, I just feel that Moutinho would arrive under so much expectation and could take longer to adjust to life in the Premiership - if for nothing else other than de Guzman speaks English and wouldn't have such a big climate adjustment to make (see Vidic's comments this week?).
Between Arteta, Cahill, Pienaar, Castillo?, Rodwell & Osman, I think we've got enough talent through the middle of the park, really is more out-and-out wingers we could do with - read that Obinna's supposed to be more than a little handy down the left, de Guzman could be the answer down the right.