I'm not sure whether it is a lot harder to create a totally new track than edit Westhill or Blackwood into some twisty long hilly track.
With Blackwood it would be possible to make some great variations inside the track, coming from the old blackwood where the tarmac is old, kerbs from 1970s and the look of the track is like going back 30 years to the new blackwood with new dark tarmac, shiny kerbs and nice grandstands et all. It would be quite a good looking experience to drive around that kind of mix of very old and very new.
Still, that being said, I would like to see new tracks over new configs, no matter how well they would fit on the current tracks or... Imho, an old historical track would be great addon. Just give us some 1960-70s cars with loads of power and less grip and you have a great venue for historic racing