The important thing to me is to get the squished-out mortar right with the shadow and all. What route should I take? Procedural, Photoshop-mania, modelling it or is there a really stupid simple way to do it?
If that texture is scanned/painted/procedural, is up to you. Scanned will give the best results, but not everyone has means to create good displacement textures (either laser scans, or any other technic).
Here’s a quick procedural test using the new brick texture from 2.78 (I could push it even further but this is just for demonstration purposes):