Seems this indeed was a problem with the registry files! I found the folder named '"Vonsnake" and deleted it. It contains my profile settings, yes? After that, the game started up properly. I needed to recreate my profile, but that is nothing. Thanks, Amaroq!

Now, for the performance report:
Version: 0.5.2, developer branch

I played through Arcade Toxic races on Cassandra, Harpstone, Aciknovae, Zephyr Ridge and Luna.
Before the race start, the FPS reached around 15-20. Afterwards, it drops in few seconds to 3, and never goes up. I can even see the lap time progressing on each frame by .33, .33 and .34 centiseconds.
Dropping down the resolution to 640x480 does not help. Neither does the windowed display mode.
The track makes pretty much no difference. Cassandra has even lower than average framerate from the beginning, whereas on Luna I had around 35 FPS before the race started, but eventually I got locked at 3 FPS.
Still though, I managed to place 5th on Cassandra and 6th on Luna. In both cases I got a Wormhole and Autopilot to help me However, on Aciknovae the Wormhole actually transported me between the laps, without completing the current one! This gave me an about extra lap to complete, which caused me to suffer enough damage (in a G-Tek) to explode on the last corner before the finish
Also, such low framerate caused Cannons to fire only once per frame, which caused its rate of fire to slow down immensely, needing 10 seconds to spend all of the ammo supply! Seems like extremely low framerate messes up the input data.
Time Trial and Practice are fine, around 45 FPS with 1080p and no special graphic effects active.
Survival has lower framerate, a bit more than 30 FPS on Zephyr Ridge. Harpstone with its snowstorms drops this to 20, but this is still playable.
However, I tried out that first campaign event, which was a Cassanda race with 3 contenders. I got 20-15 FPS there, and I could win this race on the first try (the slowdown of the AI opponents on the final lap is very noticeable). A bit low of a framerate, but bearable. Might be worse to deal with on harder tracks.

So, it seems that my computer just cannot handle full grid races any good enough, and I will have to concede for the limited number of contenders. I am eager to see this as a Racebox option!