Since the Maya swatch viewer can be painfully slow, inaccurate and limited in what it actually shows, I wrote my own swatch viewer, RenderBuddy.
Calling it a swatch viewer is a bit of a misnomer as it is really a render with a specific render layer. The UI lets you connect shaders and textures to specific RenderBuddy geometry plus a few extras that I'll discuss below.
The idea is that you turn off the Maya swatch thumbnails, assign a shader or texture of choice to a piece of geometry and do an isolated render. Since the scope is narrowed, the render times are very fast. If you have a plugin like SprayTrace, then the feedback is realtime.