TIE the whole season?
When your enthusiasm gets too far above 5, it drops too fast for it to increase so this is wasting enthusiasm.
However, TIE-ing consecutive games before the playoffs is useful.
Your enthusiasm is increased by 33% when you TIE and cut by 50% when you CT.
Everyday, your enthusiasm creeps closer to 5. The daily enthusiasm change goes towards 5 faster as your enthusiasm gets greater and greater (if it is above 5) or lesser (if below 5).
So the answer to your question: Your enthusiasm at the end of the season will depend on the enthusiasm you have right now.
Playing normal will not cause you to lose any enthusiasm (you will still have a slight drop in enthusiasm each day). Then your enthusiasm carries into the playoffs.