Song is definitely the more rounded player
Joss, Calum is right about a poacher being needed, but perhaps not in the way he means. Considering you play a false nine, your finishers are effectively the wide players, and they need to be fairly consistent with the goals, something thats not always happened. you need a wide constant finisher, who will get into the box a lot to finish what RVP and Fab create.
Funny, I remember having a (brief) discussion about this on ArsenalReport.
Walcott has the predatory finishing instinct, he's proved that this season. Nasri's improved too, and Fabregas can bang them in. The problem with Arsenal is the old cliche; they want to walk it in all the time. If they shot more, they'd score more, but as it is they seem obsessed with finding the perfect ball, the perfect run, the perfect goal.