One of the great things about WPF is how easy it is to make a fully scalable UI. The above picture is an examply of a UI i made, with live reflections, menus and images, and with one line of XAML, it became fully scalable.
How was this acheived - by placing all of my UI in a ViewBox. I can then set rules about how i want it to scale. In the above picture, I set the Stretch proerty to Fill - this disregards the aspect ratio of the UI. I could have set it Uniform, which will preserve the aspect ratio.
But the best thing about the ViewBox is that everything is scaled. So where you used Pixel heights - for example in an animation where you change the height of an object - those animation are scaled too, so nothing breaks!