I re-took the Practice N4 today.
Vocab: 34 questions, 7 wrong. % Correct: 79%
Grammar: 35 questions, 7 wrong. % Correct: 80%
Listening: 28 questions, 2 wrong. % Correct: 93%
The previous time I took it, when I was determining my level, I did as follows:
Vocab: 22/34, 65%
Grammar: 25/35, 71%
Listening: 26/28, 93%
So that's +14% on vocab, +9% on grammar, no change on listening (I got one of the same two wrong - clearly I need to practice that listening.)
Still I'm disappointed. がっかりしている。I was really hoping for a more dramatic improvement, and I'm frustrated by the ones I got wrong.