There will be Christmas decorations, the singers/dancers will do a Christmas show (probably). With that itinerary they might do it Christmas day when you leave Cabo. (On our Christmas cruise they did a show on Christmas Eve but that was a sea day.) You might want to check into what will be open on Christmas day in Cabo - may not be much shopping available. Christmas is not "over the top" on the ship so I don't think you will get sick of anything.
A Bad Day At Sea [with power] Always Beats A Good Day At Work
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014
Star Clippers: Royal Clipper 2015
Actually it is just my husband and I. The kids are grown. We also don't celebrate Christmas, but we don't mind the festivities. We have even traveled to NYC to see the Christmas tree. Just curious about what goes on.