thoughts for some form of bonus, like in guitar hero when you get so many notes in a row. this tends to be the make or break point in terms of competitive scoring (timing when is best to use it):
perhaps some random alien could try and make a landing on earth (gotta add some humour or something to break the monotony) spins around the earth several times before heading for a random spot which you would destroy as per normal controls. kinda like a twitch reaction needed, and something to slightly distract you from the main focus of the game. The debris from the alien ship falls to earth and we managed to pinch enough super fuel from the ship to give say 20 secs of super power (or super nukes) to the array which then gives them a wider effective range. so you can be less accurate/lazy/paniccy and still get top score as if you nailed it spot on.
EDIT- to use the special power when you want, press fire without a direction being pushed