Thank you all. Clearly, we have learned the hard way. Specifically, in response to 1982CruzStart, we booked the cruise fairly late. So, by the time we were faced with multiple bad itineraries, we were unable to change with the upcharge or to take a credit. At that time, we would have paid a hefty extra price to book our own airfare.
In the future, we will stick with alternative lines - as Regent's response to our problems left no motivation to use them again. Even an on-board credit (or something comparable) on the next cruise would have been enough for us to reconsider Regent. But that didn't happen.