No... I did put down faster times in the 'vert in HS (I never ran the MCS, which due to a 15% pulley mod, gets dumped into SMF) and stock-for-stock, a MINI is a better autoX car. The faster steering, stiffer suspension, better gearing and lower weight are problems the TDi can't really overcome without modifications.
On the street, the limits of the MINI are higher, but the TDi is more fun. In some ways, the TDi is the the MINI as the MINI was to the '97 M3 she had before it. That "driving slow car fast" sort of thing. I used to do MINI group runs with the TDi and NEVER got left behind in the corners. Ever. You simply can't go fast enough on publc roads where the difference in limits make a difference in speed.
My car is basically stock. I did have a Powerbox (changes the fuel mapping) in it for a short time and it was an eye opening experience. It did scary things to the power. I'm still on the fence about really modding the car since it's my DD and I get myself into enough trouble with its anemic 90 hp... Not to mention the MPG penalty - I'm not sure I'm willing to give up 50 mpg right now.
A modded car is a whole different animal. The owner of a TDi parts vendor in New England has a wagon similar to mine, except heavily modded with coil-over suspension, chip tuning, larger turbo, etc. He used to track it a lot. One of his favorite quotes came from a Spec Miata racer who talked to him after a session: "After you passed me, I realized, 'that's a diesel station wagon... and I can't catch it...' "
Lastly, the TDi has been a hell of a lot more reliable than the MCS (we don't really drive the 'vert enough to judge it - barely over 5K/yr), despite having a lot fewer miles (98K vs. 267K). It's a long story, but in a year or so, I'm planning to take the MCS off the road for awhile and do some restoration work on it. Nothing major, but a lot of little things... window motors... LCA bushings (again...)... track down and fix oil leaks (which may require pulling the drivetrain)... probably a couple of other things she hasn't told me yet.