You could aways trying stripping the paint down to original brick, if you're really ambitious. I've never done it but had a friend who did it using an "enviornmentally friendly" as-seen-on-TV gel called Ready-Strip. You just brush the gel on and let it sit and then scrape/brush off. Repeat as necessary depening on the number of layers. I was skeptical of the stuff, but he got great results so what can I say? And if you try to strip it and it doesn't work or you get sick of it you can always repaint it, eh?
Also, I liked the lego idea. But if that's too bright or "young" for you it would be pretty easy to graph out the bricks on graph paper or a computer program and create a more subtle mosaic pattern of your own using softer colors.