For that matter, the "aging" system could be applied to temples and labs. Older temples might spread Dominion faster and themselves produce the occasional advanced troop, while Labs might allow you to perform rituals for less over time, because you're assumed to have collected magical apparatus which can be reused or recycled. Better, older labs might also let you make or summon new types of undead, demons, etc. while at the same time increasing the chance for a magical catastrophy
as the "land itself over time became warped by the vast concentration of magical power pouring out, until the very waters and forests and ground itself spewed forth abomination".