Yes, it is a wonderful and very romantic idea. "Men ~ take note. Very romantic idea. If you don't know if she has the dress you want her to wear, buy her one and make sure it's a stretchy fabric so that you have a better chance at getting her right size.
Couple idea: His & Her's cell phone backgrounds of their couple pictures split to see the significant other; when the phones are set next to each other it is the whole/entire/original picture - So Cute!