Personally, I do like the idea of a small, temporary boost for the regions of nobles who attend the tournament. Even a boost based on the final showing of the nobles involved, especially for the winner.
I can see the boost being across the board, affecting loyalty, morale, and production. Is it realistic? Maybe, maybe not. But it makes for a good game.
The idea of an initial boost for the first noble, and smaller incremental boosts for additional nobles, is a good one, too. It could be added to the new baseline value, causing stats to trend upward.
