Okay, I know that you want to get 0.7 out without using another year, so consider this to be for after 0.7, if you agree and care to do it this way of course.
First, I'll propose that the number of seconds before kart removal in Follow the Leader changes after how many karts you choose to play with. If you want to play with many karts, you'd usually need more time as things get quite chaotic.
Second, I think you should get another item of the same kind when hitting another bonus box. Personally, I often want to throw an item away before next bonus box in order to get something different, since I'll often end up with not getting any more of the item I already have. That makes for huge waste of items.
It's the little things that makes a game perfect.