OK, so I'm not going to get into how tough it is since everyone knows it's a bitch given the location and angle unless you have tiny hands and the right tools (the latter a bit trial and error on my part). I did want to share what worked for me in the end with the hope it spares others my same fate.
I first tried the approach noted here http://www.nissanoffroad.net/how_to/plugs/plug.asp. I would say for those of you who haven’t done this bit of maintenance yet, don’t follow this approach. I couldn't get the 6 inch extension to work since it was too long to line up while trying to work it onto the spark plug, and even worse with my hand having minimal (OK zero) room to get it on the plug. Subsequently, my hand is a bit beat up/swollen/bruised from wedging it behind the engine a number of times in my desperation to get this sorted out.
Before I knew it the spark plug socket disconnected from the extension and found its way onto the spark plug all alone. Of course in my fiddling to get it back out to put all the pieces of the tools together to actually remove the plug, I accidentally worked the socket onto it all too well with no way to remove it (read - I'm in it to win it now; no turning back).
Tired from crawling all over the engine to get the right approach, I took a break and found myself over on XOC after not visiting in some time and tried some of the other approaches recommended on this thread http://www.xterraownersclub.com/forums.html. I found it to be quite helpful; specifically the double elbow joint and using a small mirror to see behind the engine. FINALLY!!! I had a use for my removable passenger side sun visor vanity mirror besides angling it down to stare down my date’s low-cut shirts while driving!!!
In terms of tools, I only saw the link to this one after the fact http://buy1.snapon.com/catalog/item.asp ... ir=catalog and using with a 4 or 6 inch extension; might have made a difference, might not have...dunno. Either way, the person who recommended it - a Nissan Master Tech - still said the #6 is a pain in the ass for anyone.
Here’s a pic of what I ultimately used that worked (spark plug socket, 2 inch extension, u-joint, 2 inch extension, u-joint, 4 inch extension, ratchet.):
