Wands don't benefit from elemental arrowheads. You can cast it with any weapon equipped and get the buff but the bonus damage is only applied if you have a bow or a crossbow.
That been said, warfare bonus to wand damage is of dubious value since the majority of your damage is still elemental and you're also wasting a rune slot for a damage type that won't affect magical armor, probably not something you want. If anything, it means you want to put in a 2nd elemental rune and then maxing 2 magic schools becomes pretty viable for weapon damage. It would still be an inferior approach to boosting crits for spell damage though.
The only case where I can see physical rune on wand/staff useful is if you're doing some kind of int based necromancer and boosting warfare.
The builds benefitting from this the most however would probably again be physical though, since if putting say a water rune makes hydro affect physical weapon damage then warfare/hydro would be pretty viable and boosting hydro would be more efficient than boosting crits.
