Hi!
That's true, downloading should be done only once. Also, most people's netspeed is ever increasing these days. So 40 MB instead of 15 MB shouldn't be such a great problem. In the end, many people are playing these maps, so the download doesn't seem to push them away.
You might be right about the decorative aspects of these maps (I can't really judge it, because I'm not a mapper). But for me, the visuals are sufficient to have fun while playing. Also, don't forget these maps are still in beta state (you'll find lots of betas on our server). So I guess there will be updates from time to time and there's a good chance for the visuals to improve.
In the end, originality and playability are more important than decorations. There are countless examples for beautiful maps that are mostly never played, just because beauty is their only feature.
Coco.