I know I owe people a couple of responses... I'll get to them sometime. :-(
-I think that the bird models have some adventages. First, it seems spinosaurids were no specialized swimmers, as far as can be seen from baryonychines, and would more resemble wading birds in locomotor style (although another problem: their limb proportions more closely resemble the short-limbed paddling birds!). Spinosaurines may have better swimming abilities (unknown because of the lack of limbs), but parsimony and the sail/hump do not suggest so.
Great. Now I have the mental image of a 17-m-long *Spinosaurus* paddling around like a duck with a sail on its back and a mean, mean, mean grin... X-D
Third, the longer neck may help with a source of precision crocs seem not to have.
Oh yes.
-Regarding [...] Bailey's hump hypothesis...
No. Just... no. :-)No, really, there's no evidence for a hump. There just happen not to be any mammals with a sail, and Bailey doesn't seem to have looked at squamates like *Hydrosaurus* very much.