Then number one cause of transmission failure is heat!!!!
All though honda's are very light duty cars and don't have a history of overheating problems in their tranny. A external tranny cooler would never hurt anything, it's just a matter of where are you going to put it. If anything I think an inline tranny filter on one of your cooler lines would benifiet your tranny the most since honda filters aren't serviceable unless you pull the tranny apart.