I am not sure I agree that penalties should be greater during finals - possibly fines but definitely not suspensions. If anything, I feel that the AFL takes a more lenient stand (by giving a fine instead of a suspension) during finals as they want to showcase the best players at that time to sell the game. Really, they should just be treating it like any other week when handing out sanctions. Missing a final would naturally be a bigger penalty anyway.
Maybe the bigger issue is getting the system for handing out penalties more robust. With some of the lesser misdemeanours that cop a week during the season, the AFL need to consider if they would make a player miss a final for the same offence. If not, then develop a better fine system that maybe hurts a players hip pocket more than the current system does. Yes, I believe players who earn more should be fined more!