May I suggest... although Las Vegas has seven decades of the "come as you are" philosophy, you will find your special evenings here to be more fun and memorable if you dandy up. Not only will you enjoy yourself and your company, but you will mark yourself as a resortgoer and not a down-dressed gawker.
Perhaps you will agree that staff and other guests will view you a bit differently... hosts and hostesses will pay attention to you, I guarantee, if you wear a simple sport jacket. Push a hankie in the pocket and you will look positively as One To Be Attended To.
No one here expects neckties or buttoned up garments when it is 107 degrees, as it was today. However, I submit that you will see my point if you picture 10,000 aloha shirts with you gliding amongst them, comfortable but dressy.
Naturally you must gear your gear towards your type of stay... walking? Cabbing? A car to the porte cochere? Dressy things will wilt if you walk a half block... nevertheless, I always wear a jacket over jeans, chinos, or dress trousers... if only in the air conditioning.
My best wishes for a wonderful stay here...
[On a totally different tack... it is a well-worn joke among dealers and bosses that the most beat-up looking individual is usually the one who hauls out bricks of hundred dollar bills, still in the bank straps... you never know here which ratty razorless sandal-wearer is staying in the Emperor's Suite...]