Don't quote me on this, but I think the Litchi third party app may have the ability to turn off the LED's?
You can disable the bottom sensors with Litchi.
I don't think the LED's draw much power at all and they are very important to have as the blinking lights have a lot to say, especially the rear status lights.
The flash patterns will tell you the status of the Spark without a device if you know what's it telling you.