People move to an area for a few reasons. One is the economy (i.e. jobs) is good, Two is that housing is affordable (which is partially a function of one), three is the area is nice (pleasant, low crime, etc) and four is family.

The rail line you describe doesn't help that much because nobody is commuting from Springfield to Boston (or even Worcester) on a daily basis. What the state needs to do is incentivize businesses to create good jobs in those cities like they did with the Seaport.