Changing the spark plugs, change the coils too?

I'm going to be changing the plugs soon and was wondering if I should change the coils at the same time. I bought the car used with 78K on it and have no clue if the coils have ever been changed. However I am not getting any misfires. Are misfires the only sign they might need to be replaced? Sure it's easy to swap the coils when changing the plugs, but I don't want to spend $170 to replace the coils if it's not necessary.



Thanks.