I definitely agree on what you and STB advise and I've always thought that 'preparing for a punch' is the logical way to create a tight core. I honestly haven't spent much time thinking about weight training from the general fitness perspective. Have you found any powerlifting specific exercises that carry over well to that field, or vice versa?
I think training the transverse abdominis would be useful for reducing anterior pelvic tilt by limiting distension of the belly but I don't see it having too much of a place in a powerlifting specific setting. Is that what you mean by 'gain lumbar stability'?
What's your opinion on heavy weighted sit-ups for core work as compared to things like 'olympic abs', roll-outs and other exercises that limit flexion of the spine? Most powerlifters I know personally train their abs with heavy sit-ups/crunches or don't train them at all.