I do change oil between trips to the dealer as indicated by the FSS system. I don't do anything except drain oil, change filter, refill oil. As far as the FSS service goes and what I expect them to do, nothing changes except I do some extra oil and filter changes at my expense between those visits.
As Gilly says, don't think that all the dealer is doing is changing oil and filter. My tech goes over the car pretty thoroughly on EVERY service whether it is A or B. Of course, he's my brother-in-law and friend of almost thirty years, but I expect that he does more than just an oil change on any car that rolls in his bay.
Have a great day,