First off, Boston is doing very well these days, for the most part. Anchored by the tech, education, medical, and financial sectors, it has a very skilled and diversified economy.
But hell, if we can spend pages discussing how the US could do better than historically, why not one of its more resilient and historic cities?
I’ll start with a simple suggestion: The North South Rail Link. Basically, for over a century (with a damnably long haitus in the middle), Boston has toyed woth the idea of connecting its two disconnected commuter rail lines, like many other cities around the world have. The experience in other cities doing this has almost always been very positive, but Boston, in our history, has become very skittish about big projects after the Big Dig went far less smoothly than it should have.
However, the idea originally was proposed in 1910, when it would have been much easier to do. So, lets say the political opposition is overcome, and the project gets completed (likely during WW1). As an added bonus, the plan was to electrify the passenger rail system (needed for the tunnel), which would have been another boost. This means that, when Boston develops its commuter rail system in the 60s-80s (assuming it still consolidates things), the transit system has a compact, contiguous, and all-electric system. This allows for performance more like rapid transit systems, and allows the rail system to do double duty as an express system for the subway (Boston’s subway is fantastic... by US standards).
This connection allows the surrounding towns to cope much better with the transitioning economy, and knits them together better.
With its old suburbs more closely knit, Boston might not take a distant second to Silicon valley during the 80s - its major tech firms are located out in the beltway, far less conducive to collaboration than the city core. Second place is still nothing to sneeze at, but its still second place. With rapid access to and from the major universities, the textch sector becomes even more dynamic.
So, there’s my first proposal. Any other suggestions?