Dinner menus are always more expensive than lunch menus. The skillet is an "all you can eat" deal, so for hearty eaters, there will be no fear of leaving the table hungry no matter if it's lunch or dinner.
The lunch skillet is probably not exactly identical to the dinner skillet (never had it at lunch, so I can't absolutely say) but it will be close. And it's still all-you-can-eat so if one is looking to maximize their dining dollars, the lunch skillet would seem to be a better bargain. The lunch times at WCC tend to be quieter, so another thing to consider is if you're looking forward to the antics and other goings on, lunch time might be a tad disappointing in that regard.
Good luck!