Nanoplasmonic metamaterials are rapidly finding uses in optical devices. Self-assembled soft matter optical nanostructures are straightforward to manufacture and are low cost, self-healing, and tunable. The simplest way to self-assemble such structures is to bring nanoparticles to interfaces where they can build lattices. While being simple to manufacture, these systems are difficult to model analytically. Here we develop an analytical model that is suitable for interfacial systems, that takes account of interactions of the nanoplasmonic structures at various interfaces and electrodes. The model is applicable to both thin-film and bulk electrodes, and it compares well with numerical calculations. On the basis of our model we propose designs suitable for simple surface-enhanced Raman scattering and optical mirror devices.