I can only answer #2 since I don't bother with the campaign nor any race save for my custom.

Spies are more micromanagement then *interesting*. You build one and place it on a planet to negate one building. For instance if you place it on a factory then that factory's production is zero until that spy is removed. Normally it only takes the AI a turn or two to take the spy out. Also you accumulate intelligence points for every spy you have active within an enemy empire. This is now how you gain the espionage levels. Beyond that spies don't do anything else... yet .

However if you are on the fence about getting DA I'd say go for it. There are a large amount of things that have been improved. If this were any other company DA wouldn't have been an expansion it would have been GC3. . Lucky for us SD has a slightly different philosophy when it comes to the game industry.