Sounds like Staale's figure might do it for you all in one render. I was using a .bum 2500x2500 on bottom skin layer and 1280x1280 on the upper skin layer. Since the "drops" you are seeing on mine are individual pixels on the original bum, you will need to use a really Truly HUGE map to get enough resolution for them to show up as actually droplet shapes. However, taking it one step further, perhaps this top skin layer could be individually remapped as a self tiling material which would allow you to do the droplet thing using a tiny map.