My friend is going in 2 weeks. Her 28 yo son and dil will be going to NBA Experience. I can let you know their thoughts after they return. They seem to be excited about going and they are both HUGE NBA fans. My friend bought them tickets as a surprise. It seems to be a big hit to them. We will see how well they liked it when they return.
My 31 yo son and 29 yo dil loved the Void. So did my husband and he is in his 50's. That might also be an option for you if you want to gift your nephews something. The Void is a virtual reality game at DS. One is Star Wars and one is Wreck It Ralph.
Another thought, there are some great videos on
YouTube reviewing the NBA Experience. Watching a few of them might help you decide.