As you may know, gradients like to band in 8-bit color.
Also, my lens flare looks great in 8-bit but terrible in 16-bit. (it goes from a realistic flare to a big fuzzy ball)
So can I change the bit depth of the layer with just the gradient?
Try using the compander. You'll find it under Effects>Utilities.
If you use the commander to compress and then expand the range Lens flair should look great in 16 or 32 bit and interact better with the other layers. It's all a matter of settings and blend modes. The best way to apply a lens flair is to add it to a black solid and set the blend mode to ADD or Screen. Something like this: