And, in case you didn't notice, I started this whole thread because I had no clue how to play MA Agartha and had been assigned them in Perpetuality.
Regarding the differences between Earth Readers and Golem Crafters, I think ERs come handy when you're in mid-game when the law of averages comes into play (you're more dependant on cost of upkeep and RP per gold than abilities of a single mage). That in mind, I've at least first recruited solely GCs as they're superior at least during the first year of their recruitment. Maybe when there are three castles up or so and all your battlemage/sitesearch/forger/summoner functions are filled ERs become cost effective. And, of course, during the turns when you haven't got enough money for 200 gold mage (going to be rare).