I was on this cruise and thought it was great! I'll be doing this one again in the future.
Yes, the bus ride was a pain, but also Carnival gave everyone on the ship $15obc to cover lunch in San Diego and FREE DRINKS the second night of the cruise along with an apology. Sometimes the bus ride goes smoothly, but often does not. The ship takes 4 hours to get to San Diego, the bus about 2 hours, there is a border crossing to deal with, etc. There is opportunity for things outside of Carnival's control can go wrong.
The cruise is a reposition cruise with 5 sea days and is priced accordingly. It is not a regular cruise route and would not be cost effective to add special entertainment. The same is true for Transatlantic repositions.
The only way Carnival could board in San Diego and stop in Ensenada would be if the ship returned to San Diego which it doesn't. People who did a b2b could board in San Diego, because they disembarked in Vancouver.
I have lots of pictures posted here:
Carnival Spirit Hawaii Cruise - April 2010