How about some oats or rye for a fuller body? Or some carapils?
I would go with a slightly higher original gravity for more fullness as well. 1.040-1.011 is 3.9%.
A more expressive base malt might help with the possible lack of malt flavor. I would go for GW NW pale ale malt for a flavorful domestic malt.
+1 to a lot of this. My session robust porter starts at 1.047 and finishes at about 1.018. For my non-hoppy session brews, I find that they end up a bit thin unless they finish in the high teens. I like the special roast here, but I'm thinking you might also want one or more of the following to amp up the malt flavor a bit:
Darker Crystal (to replace some or all of the C-60)
A touch of chocolate malt (maybe?)
I think 12.5% is a good starting point for the Crystal malt.