Steve, as a licensed aesthetician, I'll throw in my two cents. The product line Carnival uses is Elemis. It's an okay product. Don't expect any miracles from it. There are other lines out there that are more natural, healthier, with more pure mineral-base to them. It does what you would expect a cruise ship spa treatment to do. Have your wife enjoy herself with a facial or hot stone massage. She should expect the product push after her treatment is finished. This is where the real money is for Carnival. A simple, no thank you, will do the trick. Two truly spectacular lines, F.Y.I., (or your wifes) is Borghese and MD Formulations. She'd be better off investing in these products back at home. But, like Dave said, go for it !
Also, you will pay roughly the same on the ship for a facial as you will at home at a fine spa. Hope your wife enjoys herself!