I'm making a larger model that requires a lot of tiny detail. is there any modifier or technique to randomly generate tiny detail onto a large mesh rather than the alternative "Subdivide and extrude smaller faces"? picture on what I mean below.
Quick idea: You could use hair particles and a vertex group to option as to where the particles would appear on the mesh. You could then reference another object or group of objects instead of 'hair' inside the particle settings under 'Render'.
The red face indicates the vertex group and its weight. (I cheated and added an extra loop just behind the face) the two other grey cubes are used as the 'hairs', being in the 'Greeble' group.
You can then scale the sizes of these generated objects directly under with 'Size' and 'Random Size'.
Hope this helps, I'm sure there is other techniques.
Another option is to use a procedural texture (channeled through a bump map node) on the displacement slot of your material output in conjunction with the microdisplacement (one of the subsurf modifier options) present in the experimental feature set.
However, if you don't care about the silhouette that much (you did say the detail was tiny), or you don't want to risk experimental features, you can just plug in the procedural texture through the bump/normal mapping node directly into the normals of your shader.