Hi Ned,
It looks like no one has the answer, yet. I've traveled extensively throughout Mexico and while I've never been Cancun north I've been Cancan south to the border and I found it to be perfectly safe and enjoyable. Much better than driving.
I've taken buses up by Cabo, down by Zihu, through the interior of the country and never had any problems to speak of. Once while driving I did get pulled over by the Mexican police and extorted me for 500 pesos.
The food is incredible! if you like Mexican food and if you search out the good stuff. Some of the best food I've had is from the small food stands run by old ladies. Cheap and Good!
You can always go to an expensive hotel if you want to eat more American style food and prices.
ADO, Omnibuses de Mexico, and Primera Plus are some of the major first class bus lines.
The luxury buses are usually called Clase Lujo or Clase Executivo.I have ridden the luxury buses and they are excellent. These have only three seats across, instead of the usual four seats. The cost is about US$3-4 for every 100km covered.
Here's a link that might help:
https://www.ticketbus.com.mx/ticketbus/eng/index.jsp
Let me know if you have any more questions.