I was definitely motivated to invest more time and effort by the hope of winning the prize (along with the satisfaction of getting front page with a lot of karma).
Anecdotally, I’ve heard from a few other winners and authors that the Prize is a motivating factor to spend more time/effort on posts, but I couldn’t find public statements to that effect.
One direct example, from a December winner:
Anecdotally, I’ve heard from a few other winners and authors that the Prize is a motivating factor to spend more time/effort on posts, but I couldn’t find public statements to that effect.