I rode it last Fall.
I rode the obs car and LOVED it, as 4501 was coupled just a few feet away from my seat for the return trip. You also get a full meal service, which I think you don't get from coach seating. To me, it was well worth the extra $
At Summerville, there's nothing to see or do, so get off the train ASAP to get a good spot to watch the engine being turned. I found a good spot on the public road overlooking the table, but a spot along the fence near the gate for the track probably would work well. You can walk around the town, but most of the businesses are closed up or were when I was there. It's a nice little town to see, though, but nothing to do while you're waiting to re-board the train.
I also suggest getting on the opposite side of the track from the train to get the power being moved to the other end, as hardly anyone was there when I did that (in the 3rd photo below).
Also, GET THERE EARLY, so you can catch the locomotive coming down from the shops and being coupled. I was there with only other one other train fan, and we each got lots of good photos without other people in the way.