The problem with the Casino side quest is that it never went anywhere in terms of moving the story. The only thing it did was to bring Finn and Rose together, but you could do that a lot of ways that don't involve a huge side story. Their gambit failed, and a lot of people died. Of course, they could make it meaningful depending what they do in ep 9. E.g. Benicio del Toro could be the new Lando, or the kids they inspired could do something important. If they don't do something that brings relevance to that 30 minutes of screen time, I'll be vastly disappointed.
I'm convinced that the kid is going to have his own spin off movie in the next decade and introducing the character is the only reason they shat out the needless casino story line. I thought it was a good movie for the kind of movie it was but I would have liked it A LOT more if the casino story line had been dropped and if the imperial guardsmen hadn't bopped around and assumed Teenage Mutant Ninja Turtle poses.