Yes, wind the preload up on the rear, leave the damping standard, it's OK for most riding as it is and load makes little difference to it unless you're scaring the crap out of your pillion.
Adding preload to the forks to balance things out a little is a good idea but not requisite, for now. These blokes have more experience with the Vstrom than I so go with them, but don't discount it completely, if you find the front too soggy and diving too much under braking you could try upping the preload on the forks (so, screwing the adjusters in, make sure they're adjusted evenly, the lines on the sides of the adjusters help here).
While preloading doesn't alter spring strength it can stiffen things up adequately for more weight, it's why it's there after all.