The problem with any theoretical plan that keeps the bridges – besides the fact that they're a massive drain on public finances – is that having any kind of toll-free, grade-separated highway through the middle of the Portland peninsula is like a giant magnet for more and more traffic.
There are thousands of trips every day between Falmouth and Scarborough that take 295 because it's free, even though 95 is available and faster, because 95 has tolls. Having a free expressway through the peninsula is literally a subsidy for out-of-town drivers to bring more cars and trucks into the most congested part of the state. And for local traffic, it's no coincidence that the interchanges leading to and from 295 (Forest Avenue, outer Congress, Franklin Street, outer Washington) are also the most congested, dangerous streets in our city.
(this list includes Boston, but it probably shouldn't; instead of eliminating their downtown highway, they widened it and put it underground, so all the same traffic congestion problems are still there and getting worse).