Gravel is kinda hard to find but I know some machine who mine 100 blocks in 0,15 second vertically without stopping. That means over 6 gems a second approximately for 1%. Hell, just a quarry at max speed is kinda fast... Put a few over a desert and bam. You're swimming in gems. I do agree with the gravel thingie, though. Just reusing everything is fun.
EDIT : Then again, it'd take over... Over... Well yeah... Over three quarter of a dozen thousands, say, machines to keep up though. ;P So I figure it's still kinda valid. And there's still way to reduce that to 0.5%. Or even 0.33%.
block breaker = cobble. cobble + hammer = gravel. gravel + anything else = valuable ingots means there's an easy, scalable, hands off way to fabricate stuff. Not too different than UUM except much lower energy requirements (unless we're talking ~100 ppm tiny dust), a laggy setup, and no prohibitively difficult to obtain materials like chrome, tungstensteel, iridium, osmium, or neutronium.