How can I improve image quality when using GDAL to generate Google Earth superoverlays?

I'm using the free version of Google Earth, so in order to create superoverlays of my large TIF images I have to use additional software. Google suggests GDAL.

Using the instructions Google provides I generate my superoverlay in two steps. Here's an example:

Step 1:

gdal_translate -of VRT -a_srs EPSG:3632 -gcp 0 0 1130000 770000 -gcp 10000 0 1135000 770000 -gcp 10000 10000 1135000 765000 MyImage.tif MyImage.vrt

Step 2:

gdal2tiles.py -p geodetic -k MyImage.vrt

Those commands don't specify PNG format, but apparently that's the default because that's what I get. GDAL documentation has image quality options for some of its output formats (e.g., PNG, JPG) but I'm not sure how to apply them here because my gdal_translate command output format is VRT.

I understand that in generating superoverlays, there is resampling of the original image, and some quality loss might be expected. But this is too much. The original is so much better!

Is there some simple way to specify quality of the PNG images? Or do I need to switch to JPG or other format? If so, how?