How about more special Citadel powers that can be purchased?

Exile - Automatically throw/teleport a demigod across the map (2 minute recharge or something)

Sanctuary - Citadel acts like the healing stone (or whatever you call it).

Call to Arms - All minions rerouted to the Citadel for defense, head to the enemy Citadel if they don't encounter enemies.

Conversion - Demigods "converted" for a short time, fight to protect enemy Citadel.

Stronghold - Citadel "locks" all flags under control every so often.

Tower of Babel - Aura of confusion around Citadel. Enemies can't tell friend from foe.

Aspire - Citadel regenerates fallen towers (starting with the closest).

Homecoming - Citadel grants its demigods abililty to teleport to the Citadel for free.

Finger of God (the Sistine Chapel version) - Citadel uses a benevolent Finger of God to heal and supercharge the weakest demi-god.

Finger of God (the Garden of Eden version) - Citadel uses Finger of God to clothe the Queen of Thorns with only a fig leaf.

Finger of God (Cleanliness is Next to... version) - Citadel uses Finger of God to turn the Unclean Beast into a poodle.

Finger of God (Seraphim and Cherubim version) -Citadel periodically grants all minions and demigods wings, except Regulus.

Finger of God (Cold as Hell version) - Citadel uses Finger of God to Torch Bearer into a flaming snowball.

Finger of God (Go Forth and Multiply version) - Citadel uses Finger of God to grant Rook the power to enemies into actual chess pieces.

Finger of God (Turn the Other Cheek version) - Citadel uses Finger of God to strip Oak of his itchy armor.

Finger of God (Rivers of Blood version) - Citadel uses Finger of God to make Lord Eberus cry.

Finger of God (Two by Two version) - Citadel uses Finger of God to make Sela ride Sedna.

(Okay, the last ones aren't that serious... )