the manual hubs are a cheap and easy mod. if you have a snap ring tool it only takes about 20mins per side to swap them. and you can carry your auto hubs as spares.
as for cleaning after wheeling, i always stick the hose in all the holes along the frame rails. you'll be surprised how much crud comes flowing out. i am not sure about 2002's, but chuckh pointed out that its good to occasionally take off the fender flares and clean out the crap that gets stuck behind them.
when i am done wheeling and cleaning i usually crawl under the truck and give it quick once over. check the steering linkage, cv boots, fuel lines, and suspension stuff. these trucks can take a huge amount of abuse so breaking stuff is pretty hard to do.
find a local xterra club and enjoy yourself.