Agreed, he does tend to be reluctant to get a shot away, especially when a chance falls on his right foot. But I would also say his composure in front of goal lets him down, when you compare it to his approach in other areas of the pitch where he is second to none.
The De Bruyne comparison is spot on, like you say he is a real goal threat and for that reason he has the edge on Silva for the number 10 spot, in my opinion. If Silva can add goals to his excellent all round game he'll be even more of an asset to us than he already is.
I don't mean these comments to sound like I don't rate Silva, he's one of the very best players I've seen and I love watching him play. That doesn't mean he can't get even better though!