You are right about a lot. Ab workouts can contribute to lower back pain potentially worsen a slipped disc and cause more wear and tear. This is even more of the case when they are done in poor form. Most exercises require core strength and the more you get into intermediate and advanced lifting you find that the coaches don't even do ab exercises.

Sit-ups can help with muscle tonicity (core strength) and a little visibility but nothing helps better than fat loss around the abdomen.