There's various places you can feed something else into a shader to affect a pattern. On this one, I'd try feeding something into the mortar thickness input, as the inputs for the tile height and width could introduce distortion of the dots. I'm not sure how far you could push it before odd things happened. You also might want to use a math-node to set a minimum. If you want a sparse effect with more than one spot colour, have a look at using nghayward's technique twice, with different colours and offset settings, and combining them with a colour math node -- multiply, I think, since White=1. I'm not at my Poser machine, so I can't check that. Alternatively. for two different spot sizes, you could, if you matched the spacing, feed the output of one tile node into one of the Colour inputs of a second. One thing to remember is that there can also be distortions in the UV mapping or an item. You're trying to fit curved surfaces into 2 dimensions. So an even pattern doesn't always give an even result.