A rewind button ("<<") would be wonderful! If there is already FF (Fast Forward) buttons, why not Rewind buttons? You would go back to the part that you liked without remembering the time to start the replay from there, or open the playback again and Fast Forward to the right moment or press M and R to go back again.
Maybe a ciclic replay would help too. I mean, the file should not be closed if the replay ends. It should start again if it will end automatically so you could zero and press 9 do go fast to the part you want without needing to worry to pass that part and reopenning the replay again. Sometimes the play back at... feature may not help because you don't know the time of the part you want to see.