Not that I don't like my TA or that she doesn't deliver great service, but OBC is pretty much why I use her. I love doing the research and planning, so I don't really need her to scout out itineraries for me. Given the way these cruises are priced (vs. the resorts) and the fact that I usually rebook far in advance and usually while onboard, I have yet to get a call from her stating that she found a new discount that would save me $$$. Finally, we rarely make changes to our itineraries or activities, at least no changes that I can't do online by myself faster than it would take to email her and ask her to do it for me.
So, again, for me, it's the OBC.