[catrijn]

For a repeating action that I want a record of when it was actually done, I put the repeat on the individual item rather than the whole project. For instance, exercise is due at 9pm, repeats 1 day after completion. If I didn't work out yesterday, it hits the overdue list; based on how far past the due date is I can see how long I've been slacking. I can check the complete items for a log, although I do tend to clean out the old ones after a few months.

It might take longer to set up initially, since there's a lot more repeat items to change, but it sounds like it would fit your needs.