I switched the Pathfinder to Valvoline High Mileage dino oil at about 275,000 mi and it just made a mess on many different levels. I switched to synthetic 5w-30 at 300,000 and 0w-30 at about 315,000 and the engine has never been happier. On dino oil, including the high mileage stuff, I would burn about a quart or so every 3,000 miles. On the synthetic I burned about a half-quart every 5,000. To switch over I ran a can of engine flush (the thin oil, not the kerosene). I did the first change at 5,000 and then 10,000 after that.
Based on limited personal experience, I'm not sold on any high-mileage additives, just high quality synthetics everywhere except hydraulic fluids.
"Follow your bliss" ~ Joseph Campbell, mythologist