Most efficient way to drive a low power LED at half brightness
If I take an adjustable switched DC converter and turn this up to the point where I like the brightness, would I still need a resistor?


If you are talking about a fixed voltage converter, this will work until the temperature of the LEDs change. For example, because the LEDs are turned on and heating themselves up. As the temperature changes, the required forward voltage for a given current (and light output) changes. So this is generally a bad idea.

It is also possible to get (or design) a fixed current converter. This should work fine, but I'm not aware of any available off the shelf for 2 mA ouput.

Another option to consider is to run the LEDs at a higher current, but flash them at a low duty cycle and too fast for the eye to see.