I also purchased this Mazda Rx8 new in 2009. I have noticed the passenger dash cracking. At first it was small lines, and I thought it was the normal look of it, but over time the cracks got bigger. I went to my Mazda dealer and they told me that other customers had same issues and they are still waiting for a Mazda Recall. The cracks look horrible.
I imagine so. Cracked dash is cosmetic rather than safety, so who knows if Mazda will replace. Toyota had this problem with some models and did replace them.
You could do a search and see if there is a class action suit pending.
In the meantime you could cover it with a dash mat.