While animated GIF's are nice, there is somethings you never mentioned.
Firstly, GIF's are limited to 8 bits, so they can only have 256 colors, thus the grainyness of the images. They can hold alpha, but only 1 channel. This results in poor image quality.
Next, because this is in blender, the model may not be exactly as shown. The best example is how teamcolor is still alpha (transparency) in blender.
Also, you never set the model to 'smooth' so that you wouldn't see this blockness with the light reflecting. Glest models are automatically smoothed.
Finally, why not try an alternative by making a video of your animation playing, then break that video up into separate GIFs so to have people see it EXACTLY as G3D viewer will show it. Little more work, noticable quality.
Of course, I still support what you did. It is nice to see animations without the need to download. I usually would check others models, but when I'm on dial up, I don't unless they show the filesize and I decide its suitable. If they don't show the filesize, I won't give it a second look. Seriously, how hard is it to write something like 1.2MB or 7532 KB, etc?
Still, remember to smooth, and consider replacing the texture with a non alpha one just for that preview. Of course, do remember not everyone wants to see the unit, and will wwait until you release the mod...
EDIT// Oops, almost forgot the most important part! DO NOT MAKE GIFS OF LARGE IMAGES. While fine for still images, large animations can cause lag, and take a while to load. Thus, I would recommend a 400px2 max size. Smaller is better. If you have a really large thing, just show it as a youtube video (very easy, loads fast (though not on dialup), and can display it in the G3D viewer, as is with team color and stuff how it was, no degrading!).