Thanks - I was going off the O license authorisation as a guide. They do the 1 corridor and the 55/155?
To be fair, I was on the 1312 out of Hatherleigh and I was pleasantly surprised by the passenger numbers with 2 others boarding there and also picking up people at North Tawton and Sampford. Not enough for a decker but healthy for a bus heading to Exeter at that time of day!
I agree with your earlier thoughts that Stagecoach have done a good job in Devon, probably assisted by the positive attitude of the county council. And they do have some scenic services with the 5A and 5B up through the wilds to Hatherleigh and Bideford just a couple. Great that they use double deckers, I think there must be some interworking with the 155 but it looks complicated. They also continue to be enterprising, eg extending the 9A to Lyme Regis which I hope has been a success. The Devon Day ticket is great value.
Shame you missed out on seeing Great Torrington properly, close to the town centre there is a terrific view looking out to the south as the land just falls away to a view over Dartmoor.
Instow is odd in that the 21 sticks to the main road so you miss all the sea front yet it is really close. The 5B goes along the front and is much more scenic. Going back the 21 (I think) and the First 1 further back, used to run alternately via the two routes but I guess that got confusing and people got fed up of waiting on one road when the next bus came on the other!
The Barnstaple enquiry office was certainly open last time I went there in summer 2017.
If you choose to visit again to make up for missing Okehampton then a fabulous route is the 118 across Dartmoor from there to Tavistock. And/or one I did earlier this year is the once a day 178 to Chagford, Moretonhampstead and on to Newton Abbott. If you leave Okehampton on the lunchtime one then - after many diversions and deviations around the edges of Dartmoor - you can spend some time in both Chagford and Moretonhampstead before heading back to Exeter on the 359.
I agree with your thoughts on the 157 from Exmouth to Sidmouth, a lovely route. Shame it doesn't go to the middle of Budleigh Salterton. I did the 57 too which is a good route but when I did it one bus each way got held up at the Topsham level crossing every half hour - where the trains on the Exmouth line pass. This meant that half the 57s got delayed and half didn't - with the inevitable result. This might have happened due to some road works but I thought the timetable made this unduly risky. It may have changed. If you can make the Axe Valley 899 between Seaton and Sidmouth that is really incredible for the narrow lanes.