Gold nanoshells covered with sharp rods called "spiky gold nanoshells" are synthesized by employing a silver-assisted seed-growth method for heterogeneous nanoparticle syntheses at polymer/water interfaces. It is found that silver ions in the growth solution play an important role in forming uniform gold shells as well as regulating the surface morphology. The optical properties of spiky gold nanoshells are investigated by single-particle scattering measurements, single-particle surface-enhanced Raman scattering measurements, and finite-difference time-domain modeling. The scattering intensities from isolated spiky nanoshells are significantly enhanced compared to those of conventional smooth shells. Moreover, due to the abundant hot spots on spiky nanoshells, the SERS signal is readily observed from single spiky shells with a very small intensity variation (35%), whereas there is no detectable signal from isolated smooth shells. These results demonstrate that our synthetic method provides a straightforward way to organize metal nanoparticles into well-defined assemblies with enhanced scattering properties.