I did a WalkScore last year for Salem; I live near the train station so it's close enough. It is 92, and likely to be amongst the best scores outside North Station... My original posting is here.
I found the walkability scores for all the stops on the Newburyport/Rockport line (see below), and Salem actually gets a 94 (out of 100), which is better than all of the Red Line stops in Dorchester and all of the Blue Line stops in East Boston. Salem gets a near-perfect score thanks to such nearby amenities as a movie theater, a "bookstore" (Harrison's Comics), and a "fitness" establishment (Body & Soul Massage).
The worst score I've come across so far is Rowley Station, which gets a single-digit 6. Chelsea and Lynn each get a 75, which says something about how underserved those areas are despite having very dense populations.
River Works (used by GE employees only): 51
Beverly Depot: 86
Prides Crossing: 37
Beverly Farms: 58
West Gloucester: 12
North Beverly: 68
Newburyport (not downtown): 54