I've got one gone worn.

Is this a deal where the whole hub gets replaced, or is it a press out/in deal?  Or is it just some sorta crazy simple, incredibly cheap fix?

'02 XL-7 running gear.

All of the above except cheap
You can pull out & press in a new one with the right tools. You can also buy loaded hubs that are less work. Do you have XL7 knuckles? You should check the needle bearing inside the spindle, they tend to wear out due to the drive flanges, unless you have lockout hubs.

All of the above except cheap
You can pull out & press in a new one with the right tools. You can also buy loaded hubs that are less work. Do you have XL7 knuckles? You should check the needle bearing inside the spindle, they tend to wear out due to the drive flanges, unless you have lockout hubs.

The muffler place that did the inspection that noticed the wobble had quoted $250 for the part (total 350ish), which was right out.  Then I checked AutoZone; they only had loaded hubs listed (think it was $160), no simple bearing option.  O'reilly had both, and the loaded hub was $130, don't recall the bearing price, but the hub looked like such an easier driveway fix, I grabbed it.  They had it trucked in right after lunch, same day.  Nice. 

Then I proceeded to just enjoy the San Diego weather in St. Louis and didn't do any wrenching.

Is the knuckle needle bearing something I should bother with now preventatively, or might I just as well wait 'til it craps out and replace it then?

If it craps out while your doing 70 in rush hour freeway traffic, I'll bet you'll wish you checked it now!