From my humble experiences... With light (and sound), you can identify a 2x change in levels--but usually that would require side by side testing (set light to xx lumen, then to 2*xx lumen). Seeing one light one night, and a 2x light the next night would not be a very noticeable difference.
(By the way, this also applies to larger lights--just like a 1-2 watt output change is noticeable--a 500 watt to 1,000 watt change is also just noticeable).
A 10x difference in output is a "night vs day" type change.
From my point of view, I would rather have 2x the runtime vs 2x the intensity in most conditions. That is why multiple level LED lights are so nice (multiple level single filament bulbs do not dim linearly--as they get cooler, the output drops dramatically--thereby not saving you much in the way of battery usage).
Also, especially at higher outputs, both the LED emitters require more than 2x the current for 2x the output and the batteries are able to output less total output energy at 2x the current levels...
For a good example of battery output vs current, this oldie but goodie
CR123 battery comparison thread by SilverFox.
So, for me, upgrading lumens in an LED means upgrading runtime. In many cases, all I want is a 10 lumen or under light (with long runtimes) for knocking around in a dark space or reading something... A 100+ lumen light is just painful and distracting 80% of the time.
I think we have all gotten spoiled here... Not too long a go, a Mini-Mag 2AA flashlight was not a bad general consumer light with a few hours of gradually declining light. Now, a light 1/2 the size gives a nice beam for 65+ hours... Plus, just a twist of the hand the new LED light(s) can 15x brighter for almost 2 hours of constant white beam.
-Bill