If you need full-time 4x4 in the rain, you need new tires.
On a related note, I just bought myself a new XJ!

Picked up a '98 Sport, 4 door, 4.0L/AW4/231/8.25" teal w/ grey interior. Not grocery-gettin' grandma clean, but very clean nonetheless. 142K on the odometer, 80% tread on stock-ish tires, completely stock and unmodified. Paid $3K total, found it at a used dealer on Evergreen, had him throw in the tabs, title transfer and whatnot. I haven't taken any pics, but you all know what a clean, stock XJ looks like. At least you remember back when before you beat the piss outta yours.
It'll be a couple of months before I do anything to it, I still have to strip down my '91 and have the hulk hauled off. I've also got some rollcage mods going on with my CJ, so I'll be busy as a beaver for the next several months.
Good luck to the OP on finding a nice, ckean XJ. They're out there, you just have to look for a bit sometimes.