Thank you for the kind words! I would have liked to give the tracks a little something extra too. I tried to give them some personality, but I'm not sure I fully succeeded in that regard. I tried to have a mix between short and long tracks, I made Pulmonary Speedway narrower (not sure this was fun or even noticeable), I made Aorta a wide level (not sure this was fun), and Vena Cava had the spiral boost crazy ending you talked about. I feel I could have done more interesting design with the little plaque boosts, but all in all, I'm reasonably happy with the ~4 hours I got to work on all the levels!
If I could re-do the week, I would have probably asked a teammate to take over a few of the levels, and work with them a little bit more to figure some more interesting design ideas.
It's a little bit silly to me that I wasn't able to devote more time to the levels, since it's such a huge part of the fun of the gameplay experience. But that's the game jam life sometimes, I guess.