Well, for some parties, Stool is their only means of communicating with Underdark inhabitants who don't speak surface world Common. The character of the adventure will change radically if you're not able to communicate with anyone--it almost can't help turning into a hack 'n slash at that point.
No opinion on the traps. At my table I'd probably call it 500 for a small one (2d10 to an individual or an AoE d8), 1000 for a larger one, and 2000 or more for a complex or multi-part one. But in all cases, as with monsters, they only get XP for circumventing obstacles preventing them from achieving a specific goal or ambition--so it probably has to be a trap preventing them from either (a) getting out of the Underdark, or (b) becoming filthy rich, depending on what motivates the given character. It's not the trap per se that gives them XP, it's working towards those ambitions.