I'd say if they are not keen on doing "silly stuff" this game might not be for them. But you might be able to pick and choose cards that are used in the game, removing the "sillier" ones and keeping the ones that are more about "communication challenge". I wouldn't mess with the game any more than this. The system itself does introduce the madness card gradually - if you play 3 player there are no madness cards at the start, with more players there are just a few. You get more when you fail missions or gain specimens, and normally you only have to get the next level of madness cards once everyone is already at the current level.
Agreed, my gamer friends would insist we play it to the letter (no ez mode).