I'll share some ideas I have shared before here.
Secret clubs - These sims can gather together but if your sim don't know about the club or isn't a member of it, there's no indication they're gathering. Secret clubs cannot be found in club list unless your sim is a member of it.
'Perfect Hangout' lot trait - A lot trait that boosts club point gain to clubs gathering there. That's it.
'Lame Hangout' lot challenge - Slows down club point gain and may encourage sims to break the rules.
Now, I'll add some new ideas.
Ability to customize (fine-tune) the activity. For example, when you choose playing video games as an activity, you can choose whether or not it involves phone games, computer games, console games, arcade games etc.
More replacement clubs. Replacement clubs are clubs that are automatically generated once there are less than 10 clubs in the game. As I have seen, there haven't been more replacement clubs added. So there should be more, like knitting club, singing club, acting club etc.