Well tonight's been awesome.
I went back onto the Speed Dreams website, as it's been ages since I installed, and I decided to download "More HQ Cars etc." ...
Downloaded it and installed it, wondering whether the fact that is said it was version 2.0.0 rather than 2.1.0 that I had installed, and BOOM errors everywhere, and no cars, and no tracks... so I thought "The fuck?!" and re-downloaded everything after uninstalling.
Obviously when I re-downloaded, it was fine. All working, but only the Supercars category and a few tracks, so I tried the HQ Cars and Tracks file - BOOM errors again and no other tracks than Espie and the Supercar category.
WHAT IS GOING ON?!