Small tyres mean more ride comfort. The TRD rims added in the ativ models are quite expensive. I am told by indus sources that these rims were procured at an extra cost by the company, to make the car worthy of being Gli's replacement. Changing tyres, retaining the same rims might bring more comfort to the ride.
I believe although the height is raised, but that is done with a mathematical proportion by the company, keep it that way. It does not make a big difference, adding oem side skirts will make the car look more decent.