Depends on whether or not he used taxpayer funds, which would be pretty amusing given that Sanford was a major figure in the "Tea Party" movement.
Spitzer never used public funds to hire the prostitutes. Although he of course broke the law while Sanford didn't, at least Spitzer didn't irresponsibly leave his state ungoverned for several days.
Well under SC laws, Sanford broke the law as well.
Spitzer resigned by his own will; I don't believe Sanford's feet will be put to the fire unless he was using government money. I could be completely off base though.