The only thing "wrong" with the X1900 AIW is that it "only" has 256MB of ram. Certainly enough for most of today's games, the GPU itself is leaps and bounds better than an X300 or X1300...
There'd be no major reason to upgrade to an X1300 from an X300, you'd probably better off just buying a stand alone TV Tuner. However with the X1900 you're definitely going to excellent gaming performance with the AIW functionality.