I've gave or got six digits in the last 10 years. (I also got out).
First, you can't benefit from the nonprofit relationship. That means you can't do a financial transaction in a more beneficial way than the nonprofit could get from anyone else (or that you could get from any other business). For instance, you can't loan it money above market rates. Even if their credit is nil and no one else will loan it money, that's no excuse.
Second, when you are a director or officer, it becomes self-dealing, and a favorable-to-you deal becomes inurement. You need to seek proper counsel on this, or tilt the transaction so it is obviously not in your favor in any way. Zero interest loans are fine.
But it's not really an investment at that point, is it?
Control is a big factor. If you want control, you have to reduce or lose tax deductions. (the good news is, if you don't care about that, you have a lot more freedom; in fact there's a new structure called an LLLC or L3C that's ideal for that). I chose tax deductibility, so I have to put up with 2 strangers on my Board. It sucks.