Had ground rod connection added to my electric panel, should old ground to copper water pipe be disconnected?
No -- that bond wire could save your life!

It is very important that all non-current-carrying metal, including the cold and hot water pipes, be bonded to the electrical system ground.  This prevents highly unpleasant surprises should a wire in the dishwasher come loose and contact a water pipe!  Furthermore, this requirement is enshrined in 250.104(A) of the Code:


  (A) Metal Water Piping. The metal water piping system
  shall be bonded as required in (A)(1), (A)(2), or (A)(3) of
  this section. The bonding jumper(s) shall be installed in
  accordance with 250.64(A), (B), and (E). The points of
  attachment of the bonding jumper(s) shall be accessible.
  
  (1) General. Metal water piping system(s) installed in or
  attached to a building or structure shall be bonded to the
  service equipment enclosure, the grounded conductor at the
  service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used.
  The bonding jumper(s) shall be sized in accordance with
  Table 250.66 except as permitted in 250.104(A)(2) and
  (A)(3).


Also, the pinhole leakage you saw in your hot water pipe is a water chemistry issue (excessive chlorine residuals can attack copper pipes), not an electrolytic corrosion issue, and has nothing to do with the bonding of the water system or any dissimilar metals -- in fact, in an iron-copper couple, it's the iron that corrodes first.