I've invested enough to get the "Supporters" badge, and recently they even convinced me to adopt the "Moderator" badge. So far I haven't even ran away at top speed!
What do I get out of it? Discussion, yes, but also a creative outlet. No one IRL reads me Civ stories, but for some reason they're popular here. A side project editor for Civ3 turns out to be popular for long enough that I've worked on it for longer than any other project in my career, so it's actually kind of useful for a resume/interview story standpoint. My archival work also led to a story I can refer to during interviews, although that particular story wound up involving another forum, just building on what I'd started at CFC. And thanks to the C7 project, I can now say that my C# skills are up-to-date instead of rusty.
So, yeah, it's probably been worth the "Supporter" badge. Even if I do spend too much time here occasionally.
If I could invest to own 10% of CFC in return for 10% of the profit or loss? I mean, it would probably be an okay investment, CFC is well on its way to making it to 2050 and thus standing the test of time. But I'm not sure I'd want to turn CFC into a for-profit public corporation where anyone can invest in it. Thunderfall seems to have been a pretty good steward over the past 20-odd years; new management might actually take up that scheme to reduce the moderators' pension!