I think I'll give that a try as well. Like you say, I can't very well look at the screen while I'm firing it anyway (unless I'm in front of a mirror or something).
Exactly, any little bit adds up over time. I don't know exactly how much battery life it will actually save, but it has to do something. I will prob drop it down even more, 25%, when I get home, and change my idle brightness from 63% down to 50%. 50% is actually still pretty bright, considering the VS has a very clear screen. And if you're ever in the sun, and need to see the screen, if you fire the mod for just a click, then let go, the device lights up to 100% brightness for 3 seconds until it goes into idle mode. And of course, you can change that 3 seconds to longer.
I know when I had my sx mini m class, and updated the firmware, they added a new eco mode to the device. Which basically made the screen dim, and turn off, with in about 3 seconds after firing it. Before the update the screen would dim, and turn off, like 20-30 seconds after firing. Once this updated allowed eco mode, I went from having to charge my device after 2200-2250J used (out of a 2600VTC5), to 2600J used. So it does help.