I'm going to be the first to say... DO IT! If it solves a problem and it's a simple idea, and it lets millions of users access it, you got it. Of course not every person may hear about it or install it, but that goes for any app.
Remember, you can always improve the app later on... such as allowing users to trade coupons of equal value for other things! For example, I found a coupon on a carton of ice cream for a free ice cream at Friendly's... I was going to throw it away, until I read the odds and saw that users had a 1 in 20 chance of getting that coupon. That made me realize it must be valuable. Turns out that coupon is for a FREE $5.99 ice cream sundae. Do I really want to eat that much ice cream in one sitting?
Now, let's say you're in college, and have tons of roommates and friends, and you can easily swap gift cards around. Even with college students you don't know, just to make new friends. For a $6 movie ticket or something. So I don't have to eat that ice cream, BUT someone else can get the benefit of it.
I don't know. Let the users figure it out. Especially when you're 18 and 19 and shy, it makes it easy and fun (especially in nerdy majors) to do something like that to get conversation started.
Or let's say someone gets a $50 gift certificate to Abercrombie and Fitch, but they don't wear those clothes, or they wear Tall sizes, and that store doesn't carry anything. Should they throw it away? Why not trade it, like for a $50 used textbook.
Then, eventually you become cool within your college and also your professors give you good recommendations. It's also something that you can talk about 2 years from now when you're doing even cooler things.
Creating something is the best thing a person can contribute to society. The ONLY reason not to create something is if you have another immediate project where you can help even more people and more realistically, in which case you would create that other thing. Otherwise, creating wins. Just say to yourself that you will simply spend 2 days on it, and make it happen.