Can a wizard use a wand with a cleric spell in it (and vice-versa)

[Shin Okada]

Yeah. And if you include Ur-Priest, Divine Crusader and such in your world, some really cheap wands and scrolls become possible. Like, say, Wand of Assay Spell Resistance with Caster Level of 4, or Scroll of True Resurrection with Caster Level 8. IMHO such things should be very rare, though.