Comment 7 for bug 503577

"The real issue here is that when pressing the brightness keys, the brightness value in gconf is not updated"
I think you are oversimplifying this bug.
Well you do have much more experience than me but for me, there seems to be 3 sub-bugs in this bug:

1) Normal drivers are unable to update the brightness of the LCD, that seems to explain why step two of the workaround does not work until step one is done. Also bug description suggest that there is no way to change brightness even with mouse in gnome-power-manager, until the acpi_backlight=vendor is passed to the kernel.

2) Brightness keys are not recognized with normal drivers (I suspect scancodes could be different with vendor drivers than normal ones, but this is just my hypothesis). Still, it need vendor drivers to work, as explain in initial description. But it is also possible that vendor drivers do direct brightness adjustments directly, that would explain why gconf never see the changes.

3) Gnome-power-manager settings (set by mouse) is not saved, but is temporarily value. According to documentation, that would be normal, but documentation seems to fail to explain how to set a saved 'normal' value for the brightness. I don't know.

Searching 'brightness' for bugs result in lots of bugs, that seems to confirm that this is not only happenning on Dell mini 10. (Well, I did about one month ago, but I expect things have not changed much since).