there is an expense/impact for rewards ... but there is a great benefit for stabilizing the asset. So I'm glad you're doing it in general.
I felt like i was answering the questions about the rewards which people were asking... but it's important to give the full context so they understand the additional benefits that impact their contributions to either pool because of the introduction of a stable asset pool.
In theory If all that goes into the DAI pool is $100 beyond your contribution then they will earn 100k dec a day. So we all hope that people are motivated to move to dai. Motivations (and expenses for inaction) are indeed part of this equation.
I assume that eventually incentives like this will motivate a sort of equilibrium or perhaps more reward to those that are on the riskier pool which sounds like the eth pool?