Since your problem seems to be only at cold start, with no other symptoms at other times, I'd make damn sure that the ignition system is functioning at optimum levels before I'd tear my hair out chasing injection gremlins. The NGK's can be hard to find in stock, but most auto parts stores can order them from their supplier.
With a cold start problem like that, I'd be thinking fuel too. The fuel accumulator, or the cold start injector (leaky or not activating), or the thermo-time switch, or leaky injectors... Then again, new spark plugs are almost always worth the while -- I just wouldn't expect them to help with this particular problem too much.
I've been running Bosch F6DTC's myself (for the record, my cold starts are instant -- it's when it's warm that it can sometimes take two or three cranks). I've seen the NGKs around here, maybe I'll try them next time around.
Cheers, Oleg
