Cruise, I am thinking more and more you should try the Carnival Spirit to Acapulco, Zijuatenejo and Manzanillo. The Norwegian Star does the round, too, more or less if you prefer freestayle dining.
The reason I think this is a good fit?? These are new ports for Mom, only one tender site, 8 nights (for not much more), and true Mexico (non-tourist feel).
Check out my pics on the photo gallery -- just search under my name.
I think this sounds like a good fit -- by the way, my neice is doing this route in November on Norwegian Star for her honeymoon -- I paid for her to be upgraded from an inside to balcony -- this a truly wonderful balcony type cruise.
Hope this helps.