When I-91 was pushed through Hartford in the '50's and '60's, the Connecticut River, like many others, was a cesspool of industrial waste, sewage, and run-off. Thus, land was cheap along the Connecticut River, which is why I-91 is there (ditto for highways in many other cities).
That said, nothing is going to happen to I-91 right now as it was rebuilt 10/20 years ago. As soon as CT is done with the Q Bridge project in New Haven, looks like the next big effort will be replacing I-84 in Hartford with something. CT DOT already has a website for it.
http://i84hartford.com/