When I traded in my '00 V-10 (2-valve) it had racked up 185,000 trouble free miles. I changed the spark plugs on 50-60,000 mile intervals and never had one come out by itself. It did have several exhaust manifold bolts broken, but it wasn't leaking so I never bothered trying to fix it. Great engine!
I considered and passed on the diesel option when I bought the thing new. Couldn't help but think when trading it in that I would have just been breaking even on operating cost. So I guess it wouldn't have really mattered which one I had chosen after all. And no, I wouldn't have kept it if it had been a diesel as it wasn't the engine that wasn't doing it for me any more.