Does Smite apply to Channel Pos/Lay on Hands damage if the target is undead? What if using a Wand of Magic Missile? Anything ridiculous stem from if this is ruled this way?
Per RAW, yes. From the PRD:
If this target is evil, the paladin adds her Charisma bonus (if any) to her attack rolls and adds her paladin level to all damage rolls made against the target of her smite. If the target of smite evil is an outsider with the evil subtype, an evil-aligned dragon, or an undead creature, the bonus to damage on the first successful attack increases to 2 points of damage per level the paladin possesses.
Since Channel Positive Energy and Lay On Hands deals damage to Undead, and requires a roll, it constitutes a Damage Roll, and Smite applies to Damage Rolls of all kinds.
Per RAI, I feel that this should be something that applies to something that requires an attack roll to function, but it's not really overpowered to rule against it, since Paladins rarely use Channel Energy or Lay On Hands to damage Undead; their Smite damage for their melee attacks is usually more than strong enough.
Any thoughts on with Wands, Scrolls, Unsanctioned Knowledge, other Pally spells?
Any thoughts on with Wands, Scrolls, Unsanctioned Knowledge, other Pally spells?
There are some old threads on spells, wands etc. Search "Smite and Spells".
RAW is add smite damage to all damage roles.
You get to smite with basically any form of attack. That includes lay on hands and spells.
The real question, and actually the context of a thread I started a while back, is how does that work with multiple attacks (such as magic missile)? I've tested this concept if it's allowed to work and it's terrifying amounts of damage output.