If you take care of it, I'd say you're good for another couple of hundred thousand miles.
I am at 385,437 miles, mostly highway on my non-nav, basic 2000 LS400. Original engine and tranny, new radiator yesterday, new fuel pump two years ago from running it too often while low on gas, new exhaust and alternator last year. I've used synthetic oil since buying it used with 69,000 miles at auction for $17k in '04.