Hey,
there is a very heavy physical attribute penalty from planar madness. Making it ...not worth it, despite the bonuses.
If there was an additional +2 intelligence or perhaps other intriguing bonuses- like the Unpredictable Fluctuation on spell DC applied, it could be very interesting!
It might be interesting to add a level 1 chaos shield at the "heavily infected" mark that will get stronger as the pc becomes more infected by the planes.
Its a terrible, maddening disease that destroys people in horrific ways. Its not intended to be beneficial...