I don't know right now how to get students to use Moodle (or any other platform) more than they do right now...
But I don't feel confortable to give points to them to force the use of Moodle... From what I understood a few years ago in a class about evaluation, in theory, you should evaluate only once at the end of the learning process. The idea behind this affirmation is that if you do something for the first time, you should not be penalize if you make a mistake... You should learn first, try to use this new knowledge, practice, etc, then be evaluated.
By giving points, the first goal for the students is not to learn but to gain points. Some people say that it could even kill creativity in some extent because the student will conform his work so that he gets more points... He will experiment less for the same reason...
So I have tried this and here how I compromises on this principle :
In a 15 weeks class, I will give an exam on week 5 and 10 and the final exam at the end of the class. During the weeks prior the exam, I give homeworks, text to read, labs to do, etc. There is absolutely no points for those, only for the exam. And nearly all the students do the work!
From experience, the trick is to explain really clearly on the first day how much learning is first of all a decision that the learner has to take. Learning is the responsability of the student not the teacher. The responsability of the teacher is to provide the best learning conditions for the student. They have to make decisions every week - I make sure of that! I give optionnal homeworks, optionnal readings, optionnal labs... A student could decide to do the minimun if they are confident that they have learn their stuff... or do more if they are unsure or they want to be the best.
During the learning phase, they could propose to make change to the labs : no problems if my objectives are met! Do your own thing!
At the end of the learning process, I change hat : I become the evaluator. So I don't a double role at the same time... my role is then very clear during both phase...
So the trick is to convince them that it is the only way to go if they want to really learn... They have to get involve... That I am there to help them, not to constantly judge them for points. I will evaluate them during the learning process but just so they know their mistakes.. And this way of learning is much more fun and stimulating... the motivation come from within...
The teacher has to be convincing, he has to be very coherent... The students have to make decisions, the teacher must provide them with good one to make!
And it works! My students love it and they always ask why the other teachers do not do the same thing!
It was not easy because for me at the time, it was such a change from the mentality that I HAD to motivate my students by points... I had to go slowly, develop a way to talk to students about what THEY want to learn, etc...
So the only answer I could give you, is to try to find a real situation (not an artificial one) to use Moodle where not using it will result in a less efficient learning process for the students. I have discovered the hard way that the students will find really fast that the problem they have to solve doesn't stand on his two feet! I also find it effective to explain to the students why I made my choices as a teacher...
Part of this method, is the way that I calculate the final grade... but this post is getting way too long!
I hope that those ideas help you! Tell me what you think!