The reason there are not many observer maps (if any at all) is because they simply do not work 100% with the game engine, they are fundamentally broken and crash after you complete any games on them (No fix for this).
They do work great for testing the AI, as you can watch how it plays against itself, but other then that their is really no properly working multilayer functionality for them.
Also if you make convert a 1vs1, 2vs2, or 3vs3 it will crash when you select those map size in the maps menu (Basically meaning you can only play 8p maps if you do this)...