Aren't the houses a Wildmana mechanic while this is a module for Rife?
oups, you're right.
But on the other hand, while it is not a necessary wonder. and it is not necessary to have more than 3-4 cities with mage guild, it is useful.
I mean, when I need some adepts for "bodyI" that I just built, I won't necessarly use some hardwon promo on my current mages. I won't either use my big-production cities to build those adepts as i'd rather they build wonders, longbows, champions TIV units...etc
thus, the (almost) good for nothing cities (only size 12-14) that have some building they can build to pursue their upgrade, will make an "upgrade stop" and spent 4-6 turns in order to build the adepts. and lo.. I have 5-6 adepts with bodyI.
So, while on a tactical level you would think you need only 3-4 cities with mage guild, I think that on a strategical level, mid-late game, the investment on the CL is worth it's cost, but not on a production level, on a flexibility level.
In theory you would need 3cities specialised for siege, 3 for melee, 3 for cavalry, 3 for recon, 3 for arcane, 2 for naval, 3 for disciples. And you combien it in some cities, even with one or 2 "unit-prod city" that can build almost all units.
But in reality, if sometimes you can build an archer / longbow, a chariot/horsearcher on other cities than the "specialised" ones, it can help you, when you are in a tight spot or if you try for a wonder but are simultaneously expending or under attack. It is even more useful if you can gold-rush.
So if archery, stables and barracks cannot be free in every cities, mage-guilds can.
Take what you can when you can.