I'm no expert but I guess a modern bus system has to fulfil a dual objective i.e. to provide affordable connectivity for those who cannot maintain an automobile and the to offer a dependable, efficient, comfortable and convenient bus service to vehicle owners (to encourage modal shift and relieve congestion). The traits and features you listed above become more relevant if both these objectives are kept in mind. Efficiency in operations is probably the key to striking a balance between affordability and quality of service (that has higher cost).
Where could we find KPI's for Buses services? Do we have them? I have found this interesting paper from UCL.
It's important to measure the level of service on a particular network having in mind the special conditions of every city. On the other hand, it is interesting to see that we can find more material and technical library regarding BRT rather than buses.
Just a comment...