Haynes manual says replace spark plugs at 60,000 and do the wires whenever you do plugs. I guess take that for whatever it's worth. Not sure on the wire size.
I'm pretty certain stock wires are 8mm. I replaced mine with FRPP 9mm after two years but the wires were crap in that the connectors broke quickly after a few months in the Las Vegas heat. So I went to MSD 8.5 superconductors (after a year of FRPP wires) that I've had for over three years now and I'm very happy with them.
I like my MSDs... but I hear "Livewires" are the best. Mine are more for good performance and great looks.