Thanx for your replies guys . Some good info in there.
I just purchased a 4th gen in March (2005 limited). I absolutely love it, and can't say enough. It currently has 115k miles on it, so I did a full timing belt service and all that comes with it.
Mine originally came with the X-reas system. I was told that the right front shock was leaking slightly when toyota inspected the vehicle while doing the timing belt. They wanted $650 to do the front shocks alone (about 1,050 for all four). Instead, I went ahead and purchased the bilstein 5100s and installed them myself last week. Even if I had somebody else install them, the total for all four shocks would have come in right around $700 (quoted, not absolute).
My assessment, as some have already stated, is that at such a high mileage, you would likely be looking for new shocks regardless of the system on the car right now. They seem to last about 90-120k miles, maybe longer depending on the type of driving from what I've read. Mine lasted 115k, possibly another 10k if I wanted to push them.
I will say that the X-reas system was a great system, and felt really good for an SUV. And I mean really good for road driving. I've switched to the bilsteins and I love them for their performance. But it's not quite as smooth of a ride. So I depends on what you want out of them.
TL;DR I got a 4th gen with the X-reas, loved them, but replaced them with Bilstein 5100's only because it was cheaper.