Hey Hopdropper, not sure about correcting the watery condition once it's fermented out. Had the same issue with an Irish Stout last year. The flavors and balance definitely changed a bit for the better as it aged though, so don't lose faith quite yet.
Just kegged my version of this porter tonight. I stared with 1.066 OG and ended up at 1.012, which gives me about 7.0 ABV if my math is right. Taste was awesome. Still some noticeable residual sweetness, which is surprising considering the low FG. Slight roastiness, and very slight alcohol notes, which should mellow with time I hope.
I omitted the maltodextrin and used 1/2 lb. carapils in the last 20 min of my mash, per the recommendation of the AWESOME folks at The Beverage People, my AWESOME lhbs. Mouthfeel ended up just right.
I'll let you all know how it turns out once it's all carbed up!