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The manual calls these spacers "lifters".
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Those are the shims. Even on a 12,500 rpm Yamaha R1, the valve service interval has been extended to 26,000 miles.
In the case of the Titan for me, I'll trade it before it needs that service. Even if you don't, I'm not sure it ever will.
In any case, they don't usually get noisy. They usually get QUIET, until such time as they don't close, in which case the engine has a hard time trying to stay running at all.
The dynamics are this, when the valves close they pound on the valve seats, causing the valve stem to appear to elongate, closing up the gap on clearance.
4 valve per cylinder engines have more valve area, thus the valve lift and valve speed in inches per second are lower, extending life.
I'm not losing any sleep over this. A far bigger worry for me would have been if I had chosen the Toyota Tundra, with a rubber timing belt over an interference engine. I feel much more comfortable with the hi-vo silent chain in the Titan 4 cam engine.