I don't really see how more money is more motivating. If $1M wasn't good enough, they wouldn't be racing. Heck, promise a great route, and plenty of people would volunteer for a chance at $100k.
Also, I don't even see how, if it just the 1st leg 1st place team that gets it, that is extra motivation, as that is only motivation for that team. Starting with the second episode, the only change is 9 teams are racing for $1M like always, and 1 for $2M. 90% stay the same.
At least they should make it so the winners of the most total legs of the final 3 gets the extra prize money chance. Then, the motivation is not so much the extra money, but the chance at extra money, and that motivation will continue throughout for all the top teams.