Bonus points for maths: the new policy

It has just been reported that the Irish Universities Association have agreed a policy whereby students taking Higher Maths in the Leaving Certificate and getting at least a D will get an extra 25 points.
Aside from concerns about the possible effects on equality of access raised by Kathleen Lynch , I am curious about what incentives this new scheme provides. So the idea is to get more doing Higher Maths and presumably doing better all round. Often "non-linear pricing" generates perverse incentives.
So at the high end there is no additional incentive: an A is worth more than a B by the same amount. I would have thought there was an argument for increasing the bonus as one gets a higher grade. Say a student wants to get a certain amount of points from maths. In the past he could have got it from say a C-. Now a D will do (I'm not sure of the exact numbers). Might he be tempted to put in less effort, settle for a D instead, and re-allocate effort to other subjects? So one might predict a clumping of the distribution around D for this paper.
Take another student who is thinking of taking Higher Maths but is worried about failing. The relative penalty to failing has increased (the E-D gap in points) so a risk averse student might think "no thanks". There might be an argument for encouraging students to take the chance by giving some additional reward for getting an E (i.e. a smaller bonus).
Finally,lets say the policy is successful in attracting more students to doing higher Maths. Presumably these will be the people who are moderately good at maths. So on the lower paper we get fewer A's and B's and more D's on the higher paper. Why is this something to be so pleased about anyway?
When the distribution of grades is published next year, it will be a nice little project to compare before and after.