FYI, the "high-res" textures that I started with are, in fact, .pngs; with optimized lossless compression, the "season" images are ~20MB each at 8192x4096. The gloss and night_lights maps can be losslessly compressed to 280Kb and 600Kb respectively. The issue is less how much space they take up on disk, and more how much space they take up in system memory when the game is running. The amount of compression doesn't affect runtime memory useage much; the only thing that's really important at runtime is the resolution.
Also, if you haven't yet downloaded the high-res textures from the link I posted, wait another 24 hours and I'll have replaced them with versions that are the exact same quality, but smaller on disk (fully optimizing PNGs takes a long time, but it's worth it for lossless compression; the season images are being reduced from ~30Mb each to ~20Mb each).
In terms of what winds up in the SVN trunk, I think it should be somewhere in the middle. The versions that I attached to my post yesterday were *extremely* low quality because of the fact that I could only attach 1Mb total to the forum post. I think we can probably afford more than 60Kb per globe image in the "final" version
Feel free to mess with the specularity; there's the specularExp variable that defines how "tight" the spot is, and then there's map_earth_gloss.jpg which defines how shiny different parts of the globe are. Currently, water is maximally shiny, which should probably be tuned down.