Looks like we hardly ever had such an obvious result... But race models are hard to make, they require a remarkable level of quality, and hardly any developer is able to provide it - yet.
But there may be some undiscovered talents for the other issues. Especially, I think about "Fixes to old areas"... I am certain that you could avoid almost all invisible walls in heightfield maps, by correctly using the heightfield features. I was ... well, at least surprised, to see that you re-used an existing heightfield for the Gugrontid map. And banned half of the area, unnecessarily.
Before the expansion beyond the existing **road maps continues, I really hope that you will consider using the existing unused halves of the maps. Making and editing heightfields is simple when you understood the limits and features. I made a whole map with matching texture layer alpha maps, I just still wait for any kind of feedback about it.