Well, it looks Northampton has an okay bus system there, especially the route that runs from there to Amherst. When the Vermonter was discontinued from serving Amherst, that probably wasn't a huge loss at all, given the fact that Northampton is very close to there and there are probably many college students who take Amtrak to Northampton. I would not be too surprised if these universities have their own bus routes that bring people to the various downtown areas and train stations. I see that in Holyoke, there are some more PVTA options, especially for those people who are heading to and from Springfield.
From looking at the FRTA, it seems like the service is very infrequent. Plus it doesn't run on weekends. One of these day, I would love to spend a weekend in the Upper Pioneer Valley and would love to visit the trolley museum in Shelburne. I think for that, I would probably end up taking an Uber to get there or I also saw that the museum is also open on Monday.
In terms of predicting whether a lot of college students will use the Amtrak shuttle trains, it depends on what they are using it for. In general, college students like to sleep late and in some cases very late. If they are heading back to visit their families west of New Haven, many of them will probably prefer to take the Vermonter since they don't have to wake up very late. There are probably many college students who might have morning classes on an abbreviated day so that would also be a good reason to take the Vermonter down. The majority of college students who take the shuttle trains will probably use them to head to internships and jobs closer to New Haven and further west but probably as far west of New York City. I'm sure that the internships happen a few times a week. The other cities in Coastal Connecticut like Bridgeport and Stamford have many corporate jobs so you will probably have many people getting off in those cities who are coming from the Pioneer Valley.
The distance from Southern Maine to Boston isn't like from Central Massachusetts to NYC. On the Vermonter, it takes a little under five hours to travel from Greenfield to NYP and from Portland to Boston, it's two and a half hours on the Downeaster. Even commuting from Southern Maine to Boston on Amtrak is still very time consuming and your options are limited, especially heading down to Boston if you have to be at your job there at 8:00.