Asean citizens get to use the Asean lines at Swampy immigration. A dubious benefit to say the least as the queues there look just as bad as for other non-Thai passport holders. Beyond that I don't know of any benefits - and really would not expect Thailand to grant any benefits to other Asean member citizens. Thailand is for Thais, not for Asean people. They would charge foreigners for oxygen if they could find a way.