I no longer use a TA, however I strongly suspect the TA's which are doing well do not compete on price. Whilst you certainly have the flight centers of this world doing quite well, this is more because of their buying power, and the sheer number of sales they make.
The TA's which continue to exist and do well are those who do the value-add, not try to compete on price.
For example, the time saver TA's are are the ones who I could call up and say I want to fly to LAX next week and stay for a week and then hang up with no real additional information, and who will then go and organise my flights, hotels and car hire based on that 2 minute conversation and their knowledge of my travel habits.
Another type is the location expert TA's, they are the ones that know specific locations so extremely well, that they are better informed about a location than wikitravel. They are the ones which can plan out an itinerary as if they where a local.
The days of a TA booking a simply SYD-MEL flight (and nothing more) are over, and those who simply compete against the airlines booking engines are living on borrowed time, but as a profession I still see TA's existing and doing the value-add in 20 years time.