On FF13, I actually had decent luck with farming Plat Ingots.
I think I got like 16 of them in 3-4 hours.
Dark Matters weren't too bad either. I eventually saved, and got JUST enough Dark Matters/Plat Ingots, to make needed items. Disassemble it, make other items, disassemble them, sell everything to get "Accessories Trophy".
By then I was left with no items and no gold, so when Platinum Trophy popped up, I shut off game, and turned it back on re-loading my file before I salvaged everything.
Starcraft 2 Character Name- Aqua / Code-140 Playstation3 PSN: Matty0289 Nintendo 3DS "Friend Code"-----> 4596-9586-8808