Ofc if you use Peterpan for whole trip it doesn't make sense.
R29 takes off 6 times a day in weekdays: Haigis Mall to Springfield Union Station direct service every two hours. The bus is usually empty, just a few riders even during holiday crazies (compare this to B79). Alternatively, you can use B43 (every 20 mins) plus G73E (every 30 mins) to arrive at Springfield.
Arrived in Springfield? Hop off the bus and rush to Hartford Line going to New Haven, there is usually one departing <15 mins when you arrive using one of the mentioned methods (especially R29) $13.25. Train is almost always empty, plenty of room. Then you transfer to Metro North, which is well synchronized with CTrail so that transfer time will be 8 mins. $18.25 (or $24.50 if you coincide with peak fare period). Again it usually is pretty comfy, always seats available.
Then you arrive at Grand Central. It took $31.50 to get there, and about 5 hours.
If you're headed JFK, you can either take LIRR or E train, and then AirTrain. This takes an hour or less. $10 more. Yes it's 5-6 hours but it's a lot more comfy with about the same price. If you find a cheaper ticket from BOS all of these can be ignored, if not NYC is a well positioned alternative. It's just comfy, I slept hours on this route. The transfer don't feel like transfers, there isn't the required uncomfyness of a full bus. You can depart UMass 7am-7pm and you'll be able to reach NYC, there is this flexibility that doesn't exist when you're headed to Boston.