Having trouble coming up with reasons why I would want to play "Warpstone Excavation"

Help??

Free Power not enticing enough? If you get 3 in starting hand, that's basically 3 free Power you can divide between KZ and QZ however you like and you'll still have your starting 3 Resources to spend. It's not limited, so you can any of the other limiteds into play that turn. Sure, your Units are corrupted when they enter the zone, but that's not too hard to work around. Need to watch out vs Chaos though. If all else fails, use them as developments .

yeap... Free Power.... no one even turns down free power!
perfect for the Orc Blitz as u never plan to put anything in the KZ or QZ....
and if not its easy enough to work around...

You even can playe units in KZ/QZ because why should you defend with them? They still provide power while being corrupted.