ok, here are a few comparison images.
the PNG images are the originals, the fist dump is a JPEG version (100% quality), and the "dump_dxt1" versions are after converting to DXT5, LZ compressing, decompressing, converting back to RGBA, and saving out a JPEG of the resulting image.
LZ compressed versions of these images are 29kB and 32kB, respectively.
the artifacts visible are due mostly to the conversion to DXT5 (otherwise kind of need to write a better-quality converter...).
(EDIT: uploading seems to have re-encoded the JPEGs, they are now smaller and no longer apparently at 100% quality...).
Packed DXTn Decoder: