MMA has always been very friendly, and they are also a speeder friendly railroad. Their Derby Shop guys are pretty interesting.
This has got to be a legacy of the BAR. My lone and highly-memorable experience with 'fanning the BAR was back around '80, when the BL2's and F3's were still around. Living in California at the time, a buddy and I had a chance to do a highly compressed railfan tour of New England. We popped into the Bangor yard office for permission to look around, and they all but rolled out the red carpet. The clerk put a couple of releases on the counter, "Sign here, just don't fall in the turntable pit", telling us in so many words we had the run of the place. It was amazing - talk about neat-as-a-pin, with stored power protected under tarps, and you could nearly eat off the floor in the roundhouse it was so clean.
First-class operation, and it's nice to hear that they still run a proud, friendly operation.