Why would Stagecoach be more suitable than Northstar?
My understanding is the 873 is being quite well used to Barnard Castle land Teesdale. Though I do agree a service into Weardale on Sundays/Bank Holidays would be nice.
Every 30 mins to Beamish Museum would seem overkill, especially as it is possible to get there on ordinary bus services. (That is "real life" bus users behaviour - I heard people waiting for 874 chatting about how they normally visit Beamish by a simple change to 28/29 at Chester le St.) But I agree in peak season a regular service direct from Durham on other days would be nice.
But we need to remember that all these are heavily subsidised...