I dont think that it is a great feature that will attract more people, because there are many other sites offers the same surveys/tasks with higher rewards. And I think this feature is out of the basic concept of the site.

@OP : you need to do more than this, adding new "free earning" feature is not the best way to attract more people. Heavy promotions like what arallmuus said is better rather than "free earning" feature, but of course you need to spend much money on it.