you asked...
"I can see no structural compromise to the boat with the bridge taken out.[Chorus: hi-ho any engineers amongst us?]"
actually, there are two parts to this story:
1) the bridge was under a bending moment because of the forces on the mainsheet. it performed the function of keeping the two parts closer to horizontal. and really, the vertical parts ofteh bridge are the work-horses here, just like in a steel I-beam. without it you will see much more flexure of the two posts, upward, and the most severe flexure will happen when one of the two sheet-halves is exactly vertical from the deck (when the boom is right over the post) the degree of flexure, i don't know, i could run a few calcs if the moment strikes me and if "Marks handbook" has values for shear strength of fiberglass.
2) the bridge was in compression. the two halves of the mainsheet angle toward each other and that component of the forces puts the bridge in compression. this means that the posts will have much greater flexture toward each other (in addition to the upward motion). this is greatest when the main is between the two posts, but is always evident regardless of boom position.
some back-of the envelope calcs will some reduction in ultimate strength and increase in flexture, but really some Finite element analysis will show how much the surrounding structure supports the posts. attached is an image that i might use as my b.o.t.e. calcs.
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