We have a 6.3.5000 site where all forms were recreated and all forms are currently emailing. They are also all writing the trace.log error and adding the funky sf_notif records so there's not an exact science to what's going wrong. The recreation seemed to fix it though.
Another 6.3.5000 site has one form, that was recreated, and it is doing above except was not emailing. I ran your script and it started working. I just updated it to 6.3.5029 hoping that will help.
This same site we deployed to a client environment and their smtp security wasn't correct, yet no error logging in sitefinity. Just happily said success. That and the form issue made an underquoted deployment a joy. I added a test aspx email page that spit out the error. If there still is an issue, this seems like a very high priority fix. Glad it logs the form responses in the db OOB at least.