This guy has more than a few opinions...
http://www.avweb.com/news/pelican/182544-1.html
...but their his opinions, if you listen to em, listen because they make sense not because of their "experience" (same rule of thumb for anyone... 1000hrs or 30,000hrs - not much difference when it comes to operating pistons and 29,000hrs out of the 30 are in Jets
The GFA also had some interesting notes on aerotowing and engine failure rates on engines that idle and descend at Vno compared to those at 2200rpm or higher at Vno.
My advice... run the engine the way the owner wants the engine run. It's their money, they're the ones that pay for the maintenance, it's their choice... even if you "know" better.
If it was my engine, I'd care about climb and proper use of cowl flaps. Cruise and Descents, honestly... what are you going to do at 29" and/or 75% or less power. That said, there's a lot of inertia in that engine, be gentle when you do make changes dont rip the throttle out of the firewall. Thing I'd be more concerned about is running it often - look at how many Flying Schools regularly make TBO, and look at how many Taxi's get significantly more km's by keeping the engines going 24/7 even when engines in both environments get "abused" signfiicantly.
My two cents and *more fuel on the fire*