Mazel Tov! Neither of my sons enjoyed the typical DJ centered Bar Mitzvah celebration so we compromised. We did have music but we also brought in lots and lots of games including ping pong tables, basketball games, large screen video game displays(the horse racing game generated lots of excitement)and a black jack/poker table. Basically the boys played the games and the girls danced nearby. During the cocktail hour, the kids engaged in wiffle ball and hula hoop contests. The kids earned "Daniel dollars" for participating in and for winning the various contests/games throughout the evening. At the end of the night, they deposited their accrued dollars into three different buckets labeled with the name of a charity. My son would then donate to the charities based on the "Daniel dollars" deposited in each. Although all rather low tech, low budget, it worked. Both the kids and adults had a great time competing and playing together and seemed motivated to participate by the mitzvah component. If you are interested in tying both the ceremony and celebration together with a sports theme, click
here. I have also been to some fun Bar Mitzvahs where they brought in professional entertainment: G rated comedy routines, animal tricks, and magic shows. Personally, I would skip the dinner mystery theater -- in addition to possibly being inappropriate for the occasion, I think there are too many people and the kids have already sat still through a long service once today.
Best of luck!