
I think for client side settings, you can also use the command resetvar <varname>, maybe that's more convenient here. Note that getvardef will round off defaults of floats, while getsvardef should be okay for strings and floats, too.
I always thought the screenshots are lossless, as the pngs are relatively large.
For the resolution setting, wouldn't it be advisable to set it to the desired size of the screenshot, so no scaling is needed?