On our recent transatlantic cruise on Norwegian Jewel there were no lines at all in any of the restaurants. I think that we had to wait for about 5 minutes outside one of the main diningrooms one night but all other times, no lines.
I do agree that it´s not necessary to go to the specialty restaurants, the food is good in the main diningrooms, but it´s nice to go to some of the specialty restaurants too. We went to Cagney´s, Mama´s and Le Bistro (twice) this time and the experience was great. We had Cagney´s Banana Foster Flambee for dessert at Cagney´s and that only was worth the extra 20$!