We use a TA mainly to not have to park on the phone for ages. Plus she knows what to ask, has had many useful suggestions, we arrange travel insurance through her and she's a single point of contact for any issues or concerns. We don't get much in the way of OBC or gifts but the knowledge, time, and peace of mind that comes with someone having my back is good enough for me. She told us about a new lounge that we had access to in the airport for our last overseas trip that I hadn't known about. It was amazing and a great start to the trip; I would never have even looked or thought to look for it. Totally worth it IMO (plus we got cancel-anytime addition to our trip insurance for no extra cost because of booking the flights through her and she advised me to hold my flight booking for 24 hours while we were deciding on whether to book that one or not because of information that she saw in her system and it doubled in price the very next day so we got it at the original price). She also lets me know about upcoming things, price reductions, special promotions, etc. so I don't have to monitor it. And she has lots of information about potential new places or trips to try that she knows I might like.
I rarely make changes to anything that would require a TA to intervene so that's not an issue for me and she's very responsive via e-mail and only a 5 minute drive from my office.