Here is a little excerpt for the book for you, you know that book that I am still editing but hope to have published in the next 2 weeks…!
Whist basing the value of the reward on a user’s personal investment is important, it is also important not to lose sight of why you were gamifying the system in the first place.
Normally it is because there are certain actions or activities that you want to encourage the user to perform and complete. That being the case, you have to sometimes consider how valuable the action is to you, not just how much effort it is for the user.