Speaking for myself, I'm happy to volunteer for small non-profits, because they really need it, and ten minutes of my time can really make a difference (I just translated a 100-word paragraph about an award from German to English, for example).
But Sparked themselves are a for-profit venture. I'm not 100% sure that's going to be viable, but I'm not willing to give them my time for free if they're going to turn around and make money off it.