Is it normal for LED strip lights to dim slightly at the far end?

Yeah, that dimming and color shift at the far end is textbook voltage drop. The copper traces in the strip itself plus your feed wire have resistance, and the further the current travels, the more voltage sags, so the last LEDs get less juice and run dimmer. It shows up worse in white because you're driving every channel at once, which is when the strip pulls the most power. On two metre runs the strip traces alone are usally the culprit. The fix that works best is feeding power at both ends of each run, so solder or clamp a second feed wire at the far end too. That alone usually evens things out completly. Thicker feed wire from the controller helps as well, but end feeding is the big win. On the brightness cap, it's not a myth. LEDs running cooler and at lower power genuinely last longer, and heat is what kills them. Running at 50 or 60 percent means they'll outlive the rest of the install. Just set the cap in the controller settings so a houseguest fiddling with the app can't slide it up to full by accident.

As for leaving them on for hours in the evening, that's totally normal use for this kind of setup and nothing to worry about, as long as your power supply has headroom. Don't size it so the strips run it at its absolute limit. A supply loafing along at well under its max stays cool and lasts years. Feel the case after an hour of runtime. Warm is fine, too hot to keep your hand on means you need more headroom or better airflow around it. One more thing from experience with under-cabinet strips: check how the fixtures mount before you button everything up. Those enclosed triangular housings trap heat, so a bit of ventilation and keeping the supply outside the fixture goes a long way.

Did the same thing with some bar lights I salvaged a couple years back, capped them around half and they're still going strong. You stop noticing the lower brightness after about a week anyway, your eyes just recalibrate and full power starts looking like a spotlight.

One thing I'd do before mounting them: measure the actual current draw with a cheap multimeter at your capped brightness. Spec sheets always overestimate, and knowing the real number takes the guesswork out of picking a supply.

Same experiance with the eyeball recalibration thing. I set my kitchen strips to about half when I installed them and within a month I honestly forgot they weren't on full. One thing I'd add is to bump the cap down in small steps over a couple weeks rather than going straight to 60 percent on day one. Mine felt too dim the first night and I almost undid it, but easing it back in chunks made it painless. Also I stuck a cheap thermometer strip on the fixture housing after a month and it barely gets warm now, which was good peace of mind before I closed everthing up.