If all goes well and there are absolutely no issues with your vacation, and you enjoy booking stuff yourself, for sure the benefit isn't always there other than OBC if they offer some. BUT, if you end up in our situation a week ago where they call to cancel 72 hours before your cruise, and 24 hours before you were due to fly out? Yeah....definitely happy we had booked with a TA. Many reports of people on our cruise who used TAs who had rebooked for very near future cruises (or had 100% of the rebook chaos handled by the TA), some barely even knowing it had been cancelled and the TA already had everything sorted out for them. Mine was actually notified after we were, but looked after all of our flight stuff and such. She was still sending emails at 10 pm Thursday night as she was helping us to try to sort out whether or not we wanted to go/do something else instead (last minute), and spent 3/4 of the day Friday trying to sort out more stuff for us. If the pricing works out to be the same or close to the same, hands down would go with the TA for that peace of mind. If there is a significant savings not to, then you would have to weigh the pros/cons. But we are now 1,000,000% yes for a TA after our experiences over the past week (and I am a "book everything myself" kind of gal as well). And the one we use is just a little local office who doesn't even offer OBC, but is super awesome and totally worth it.
Just our $0.02, anyway.