According to @jeff_foust, during the press conference Elon said "won't hold up CRS-3 launch to install legs on F9. Schedule driven by upgrades to Dragon. Probably Feb '14 launch."This indicates to me that the next dragon to launch will already have some upgrades, presumably carried over from dragon rider development. However, according to the Falcon nursery article, "According to L2 information, the only noticeable differences in the Crew Dragon weldment are that the aft cylinder is a few inches longer than on Cargo, and there are clevises machined into the edge of the forward bulkhead to receive SuperDraco thrusters."This information indicates that the cargo version, at least for now, will not have the superdracos and has a different pressure vessel. That means it is different on the inside layer, the outside layer, and everywhere inbetween (differently outfitted inside, different fuel storage, different engines, different space allocations between the skins, etc.).So there can't be many similarities right now, but the first statement indicates that there is some change and is still valid.