And don't forget, this is not a visa like a sticker thing. You are getting stamped for 6 months.
6 months visa for 10.000 baht plus a muay Thai gym, a cooking class, a dental clinic makes around 500 dollars to 1000 dollars at least, is pretty good as Thai economy is not looking good these days. I'm and world bank estimates that economic growth of Thailand will be around 3 to 4 percent next year which is not a good number for Thai economy.
that's the question the people don't want to answer. Of course, the immigration will definitely ask for more papers each time you want to extend your stay for another 180 days. It should be like this and must be like this... people don't want to think about this and want to imagine the government being stupid and handing out 5year visas to everybody enrolling into a 800 dollar culinary course, muay Thai course or for a 1000 dollar dental appointment.....
Thai government will probably ask for nothing when you want to extend your visa (get out of Thailand and come back again but before that pay 10.000 baht for extension). This will probably continue until the tourist numbers come back to the desired levels. After tourism recovers (if it does), we will see what's gonna happen.
Interview is a normal process and they do it randomly to make sure that people understand they can be interviewed anytime anywhere... I heard that it happens a lot in walk-in applications..