If you already have an aluminum road bike, I would buy a carbon bike such as Defy Advanced. Otherwise, it isn't worth upgrading just for better components and disc brakes.

I bought 2015 Defy 1 because it was my first road bike, I need something affordable for a beginner, I wanted v-brakes on a road bike (lighter = better), and it's significantly cheaper than 2016 Defy 1. I bought it for $1400 canadian tax in, but 2016's will be $1800 tax included.

If I were you, I would keep riding it until it's really worn out and then buy a carbon road bike.