Diamonds are worthless to me. I'd trade them 1:1 for AE quartz or 1:4 for copper if I could.
I know what you mean. After I got the required diamonds to make an enchanting table, draw plate, saw and a few other machines, I stopped needing diamonds. I have half a stack right now with nothing to use them on. I still need plenty of iron and copper however. Those always seem in short supply.
AE quartz normally gives 1/1 of quartz and dust. You can silk touch the ore and put it through the GT grinder for 10 dust, but a much better option is to use a fortune III pick on it. I received oodles of quartz and dust out of it, and could convert the crystals for way more than the 10 dusts from the GT grinder.
Back to the original question. The only method I know of getting gunpowder that hasn't been discussed yet is using thaumcraft to manufacture it. Unfortunately, I know no way to automate it, and the extra aspects released would add a lot of flux to the environment unless you have already gotten pretty far down the research path. It's not feasible for the amount of gunpowder you need for iridium plates.[DOUBLEPOST=1365484148][/DOUBLEPOST]hmm.. You might be able to use the monster spawner block from MFR. I believe you need monster essence (which can be taken from an easier to acquire mob), and a specimen in a safari net (or pok-e-ball). Haven't used MFR much, but I know it has some strange machines that might be useful for this.