I've been playing Warband vanilla for about 1000 hours now, and just noticed a sneaky way to spam tournaments. Can't find any reference to it anywhere, so thought it may not have been noticed before. Also, probably irrelevant for better players, as it's mid-game and I'm guessing most people would have plenty of cash/renown by that stage, but anyway:
1. Start a feast in your city.
2. Enter/complete the tournament.
3. Go into the castle. Piss off some lord that you don't want as a vassal.
4. Exit city.
5. Re-enter city.
6. Ta-da! New Tournament.
Seems that the tournaments are triggered by lord events, similar to villager events, allowing you to have as many tournaments as you have lords to dismiss.
Main advantage would be to quickly build town relations.
1. Start a feast in your city.
2. Enter/complete the tournament.
3. Go into the castle. Piss off some lord that you don't want as a vassal.
4. Exit city.
5. Re-enter city.
6. Ta-da! New Tournament.
Seems that the tournaments are triggered by lord events, similar to villager events, allowing you to have as many tournaments as you have lords to dismiss.
Main advantage would be to quickly build town relations.

