Yes they did. I was there this morning, Bangkok. Both me and my wife had to produce TM30 proof else they would not proceed. Others have not been asked. But if you get unlucky and are asked, but do not have it, you will have wasted your time going. Better to be prepared with it, and bonus if they don't request it. 😉
Yes. I just extended this morning and was asked to show my proof of TM30 registration. There are stories that some were not asked, but if you are unlucky to get asked, you will have wasted a trip as they won't proceed without it.
I don't know. You can ask the person who was fined in this other group. Look for the post by Jai Cutler, then scroll down the comments to find the post.
Better to be prepared and not need it, than to be unprepared and get screwed. In another group, a guy was fined 800baht for failing to register and had to pay it before they would process his visa extension.