1. Raised platforms would allow using automatic doors and all-door boarding. Right now, doors can't be automatic because you don't know which ones board at platform level and which need to have the builtin stairs dropped down to track level. As it is, not only does it take time for a conductor to drop the stairs, but staffing is a major part of the T's operational expense for each ride.

Also, the passenger throughput per door is higher when they can just walk off, instead of having to teeter down stairs. (Not everybody can just hop down the stairs)

Oh yeah, frustrated passengers opening the door and lowering the stairs themselves is a dangerous no-no.

2. Electric trains accelerate and decelerate much faster, cutting time off the trip. They have more rated HP and can "burst" up to something like 2x the rated HP when accelerating from a stop.

(Except on those fun fall days when the train slides on the wet leaves...)

Source: personal experience as an MBTA commuter rail rider (reverse commuting to Concord) for four years, former occasional NJ Transit rider (on the electrified Northeast Corridor)