Your girlfriend might claim she loves sneakers, but she probably would love a pair of super expensive heels. If you buy her a pair without her asking, she's going to definitely re-pay you--with a pair of sneakers. A pair of Christian Louboutins cost way more than a pair of New Balance 998s. But it will do wonders for your relationship and sneaker collection if you buy your girl a pair of Red Bottoms.
Buy her the investment (and pricey) heels that she's always wanted.