I'm sure any of the ladies on OhMy would love gift cards...
But seriously, gift cards? You want to use rewards points to pay for sex? Here's an idea, instead of paying for gas with cash, use a gift card, and then use that cash at 100 cents on the dollar to buy companionship.
Substitute gas for any other product.
There are some things gift cards are good for. Presents for people you don't really care enough about to put thought into shopping, giveaways at silent auctions, rewards that you can buy something you wouldn't normally buy.
Sex is not something you use a gift card for.
I do remember a few SP's that have had frequent flyer type rewards in the past, and certain parlours that had things like "fifth visit free" rewards, or discount pre-paid room fees, but that takes a lot of trust to either trust that you will ever see the rewards earned, or use the pre-paid sessions before they expire or some how get lost.