Stereo layers are pretty limited, since they are composited by the VR runtime. I think the better option is to improve the quality of the 3D widget component.
The main issue with the widgets is that it gets rendered in a static resolution without mipmaps, so it looks awful when it gets scaled as the player moves. One way to fix it is to modify the component code to make it generate mipmaps when rendering:
https://hollowdilnik.com/2021/01/09/widget-filtering.html
I’ve been thinking about it, and a more performant option might be to dynamically change the render target resolution to approximate the screen space resolution. I haven’t tried it yet though.
The quality can be further improved by adding shader-based supersampling in the material.
https://forums.unrealengine.com/t/msaa-3d-widgets-horrible-jagged-edges/138040/8