Did you happen to enjoy the mastermind challenge at all? If so, I'd recommend you find a new group and help them get it done too!
The missions may stay the exact same, but fresh faces (sorry, voices) with a good attitude can keep it interesting, I've found.
I actually enjoyed doing the CM Challenge, I want to help more crew members to complete it but I want to get a microphone first, makes communication way easier.
Don't get me wrong, I'll still enjoy the game, I'm still gonna fire up the game once in a while to help members of my crew to sell and the like, I'm just taking an opportunity to also play other games that I have.
Also, I still got the Elite Challenge left!