I definitely see the connection between people with Aspergers, especially if you look at the episode Data's Day. But Data is not a human with Aspergers even if some of the language issues are the same. There's a whole lot bigger difference in complexity between being able to use slang and being able to use contractions. Slang requires an emotionally intuitive grasp of metaphors. It doesn't sound as aesthetically clean and discrete as saying 'can not', but contractions are literally a search and replace. There's no aesthetic comfort issue with Data, and he has shown a full grasp of far more complicated grammatical rules than contractions.
I would guess the only reason Data does not use contractions is that the producers thought it would make him sound less robotic.
Also, even though Data has trouble understanding or predicting emotions, I've seen no indication that he has trouble looking at somebody's face and guessing which emotion they're displaying.