More RPM's equals quicker wear. Now if you only run an engine at idle/low RPM the rings will wear the cylinder walls to a certain area on the engine the moment that engine see's higher RPM you could crack/break rings because that piston is actually moving further up the cylinder (rod stretch, upper and lower rod end play, piston pin play). I would run the engine how it was meant to be ran (cruising RPM) that will get you the most life out of the motor. Running WOT all the time will surely wear the engine out quicker as it is rotating more forcing the piston up and down the cylinder bore more.
Its a bit of a double edged sword. Also car engines utilize a transmission which allows the engine to be ran at a more constant lower RPM. Boat engines take a beating no matter whether they are a Inboard, outboard, or I/O, they are usually ran at the upper end of the RPM then shut down quickly (4000 rpm to idle) where a car engine is ran at the lower end (2000 rpm to idle).