That 4:54 departure from BOS makes for a tight connection in EWR - just a couple minutes over an hour. Might be OK, but if there's a delay you could be stuck until the next day. I'd go with the 3:20 departure instead which would give you 2.5 hour cushion to connect to the same BCN flight at 7:30. You could burn your one time passes at the United club while you wait.