well, it seems a very un-economic strategy, because

you need to invest in

  a) physical items (paper, glue)
  b) human workforce
  c) transportation (you need to get around town)

and also

  I) nobody uses QR codes

  see http://www.google.com/trends/explore#q=qr%20code%2C%20qr%2C%20&cmpt=q and
  http://www.google.com/trends/explore#q=qr%20code%2C%20qr%2C%20mail&cmpt=q

i run a quite popular create and read QR code website http://miniqr.com, and well let's say i won't get rich (for this sideproject)

mail spam works because it's cheap to distribute, physical QR-codes - not so much.