I do remember reports of the “superdollar” being one stimulus to redesign of the more popular currency, that was accompanied as a concern with advances in the graphical reproduction capabilities becoming more widely available to the populace.
But in my perception I’l have to echo what Whack-a-Mole and flowbark seem to be saying: in physical terms it would be one hell of a job to actually perceptibly knock down the value of United States currency with cash.
An ancillary thought occurs: as long as the funny money stayed away from banking institutions than can detect it (i.e., stayed in the “Third World”), might a flood of such actually expand the world economy a little bit?
I think counterfeiting cash can benefit the purveyor in the short term, locally or regionally, but a global attack’s effectiveness is both unsure and unlikely IMHE.