Well, the largest problem with making the neck bigger is the spine itself. As well as the shape of the secondary hull. HOWEVER, moving the top end of the neck to make it wider, and into a V-shape, as server has suggested, actually alleviates the problems of the Impulse engine being too small, and the neck being too thin in the back. Plus, it matches the transition from the Ambassador-style neck, to the Galaxy-style neck much better.
So yeah, it's a much better idea. My apologies to Server for misunderstanding his suggestion.