Good point. Though I then raise you one 2002 Nissan Pathfinder V6 with a broken thermostat housing. You basically disassemble the uppder part of the engine (minus the heads) to change a stupid little part.

So you're saying that as long as I'm taking the heads off my 2001 Xterra, I may as well replace the thermostat while I'm at it ;-) ISTR it's the same engine.

Definitely do so. Along with all the cooling system hoses. Problem is those hoses are expensive, and will add about $200 to your parts tab. Worth it, though. Wait, I would actually replace the actual thermostat housing due to corrosion. Old coolant is a bad mother on your cooling system. Make sure to also flush out the radiator with running water.

Oh, and since these are aluminum parts, go to a Honda auto parts dealer and ask for a tube of Hondabond. Its a silicone dressing that is 100 times better than anything available from Pep Boys. You want to make sure your parts seal properly.