This post isn't strictly about a debating event but it could be a useful tool for people to practice their strategic thinking in debates. Also debaters used to thinking strategically about proposals may be in with a good chance of winning.
Wikistrat is holding it's first International Grand Strategy Competition later this year and there's a strong crossover between the skills of debating and this tournament, despite being in a written format.
The whole event takes place online, there are no entry fees, and the team ranking #1 will receive a $10,000 USD as a cash prize.
Ideally participants will come from an international relations or political science background as they will be proposing country strategies and foreign policy.
More information and to register interest: http://about.wikistrat.com/strategy-competition/