I would never have thought to think of the Aethos as a climbing bike. But if it's lighter than what you have to do those climbs with currently, then I suspect you'll like it for climbing and if the difference in the position it gives you over the Roubaix is okay for you, then it'll probably be your goto bike and the Roubaix will just sit in the corner.
Geometry wise the Aethos is more like the Tarmac. So it's more aggressive. Which is good if you like that, and I do since to me my Tarmac is the most fun bike I've ever had. However if you don't like the lower handlebar to saddle position that it will give you over the Roubaix, then you might be tempted to do things that look ridiculous to me in an effort to get your bars higher.
In the grand scheme of things, if you want a new bike and can easily afford it, then just buy what you want, even if it's just the color you like.