With regular oil changes (even conventional,) I've never had an engine fail due to lubrication or wear. Either I get tired of the car/truck and sell it for something different, or something else expensive breaks that makes it not worth fixing. The engine itself (in all vehicles I've owned, and there have been many) is never the deal breaker, and lasts as long as I want it to.
I just don't see the $$ vs. value perspective in these engine flushes. Even the extra $$ for synthetics is still a mystery to me, even though I still use synthetic (usually Autozone specials.) If I was dead set on an engine going as absolutely far as it could, I might try the expensive flushes and such. But then again, some ignorant driver might total my car when I've got it to 300k. You won't get anymore resale value out of a car by telling the buyer you used an engine flush every oil change... Just some things to consider...