Nothingness:
Extending the 50-move draw rule in chess up to 100 moves for some situations was experimented with for a few years and proposals were made to extend it to a greater number of moves for other situations. The results of those experiments were to reestablish the 50-move rule. Whatever conclusions you or others may come to for a greater number of moves for an Espionage draw rule, there will be those who will conclude that the number of moves should not be increased or that it should be decreased.
As in chess, the purpose of the rule is to keep the game advancing towards conclusion.