I've been researching this lately. It seems that the primary advantage of inflatable PFDs over the lighter foam ones is in packability rather than weight. A salient issue, as my foam PFD is just an odd shape to put in a pack. On the other hand, the paranoid part of me likes the foam floatation, and a PFD makes a great pillow.
As for meshing well with the spray deck, I found the main issue with a stock PFD is that the back would interfere with both the backrest and the deck. The former would push the PFD up, which would then in turn cause the PFD to push the dec down and let water in the back. Hassle. I ripped open te bottom seam of my PFD, pulled the foam out, cut it in half, stuck both pieces up into the upper part, and sewed it back together. This solution has worked perfectly, with no downside.
Still thinking about bladders to put inside an ultralight infltable PFD for wilderness trips without gnarly whitewater. Wine bladders. Camelbaks? We shall see.