Having direct rendering enabled is not enough to determine if 3D acceleration is working. You really need to check the OpenGL renderer string as well:
glxinfo | grep -i render
Having said that, you probably do have 3D acceleration enabled. Your Xorg log file does look good and 3D acceleration should be working on your GPU out of the box. It's quite possible, however, that the video card and drivers just aren't capable of decent acceleration. The Xpress 200 GPUs are rather low-end, as far as mobile GPUs go.
You could run supertuxkart with the environmental variable LIBGL_DEBUG enabled:
This will print a few lines of debugging information which would let you know if there's some other problem with your driver setup.