We were on the Elation last summer with Lisa P and her family. It was a 7 night cruise. The Elation has not received all the upgrades and still has the original pools and water slide. It does have the (not much) serenity area for adults. My favorite place to get lunch was the Mongolian stir fry station on the pool deck. The ship appeared to be in great condition although the decor dates it.
I don't know how Carnival handles back-to-back passengers in Mobile when it comes to Customs and Immigration. I suspect Carnival will have the b2b guests meet up at a designated location and they'll usher you through the process and issue your cruise cards for the 2nd segment, and you do not go through the terminal for check-in again. Thus, making a run home will probably not be doable.