Hmm, 75 GB cost, 1 GB maintenance. Assuming 3 rule/create actions a round, and you would otherwise pay 2 GB a pop to get the same bonus, the payoff is in 15 turns...
If you do one such action a season (say 1 realm spell, 1 create/rule, 1 diplomacy) then the payoff is a very long way off indeed.
But then there are court actions - which with the support of the local law holder could become very handy with a further +2. The temple domain with a cathederal then recovers from a contest war very quickly, even though it is reduced as easily, the cost and ease to rebuild is far lower.
Potential other benefits if it is considered over priced:
* social - big boasting point
* add a point or two to the regency generated by the church (not much use due to topping out, but meh)
* prevent the home-province holding going below 'x' unless the cathederal is seized
* holdings are treated as one level higher for realm spell purposes / caster is treated as 1 level higher.
I think though that the idea is that very few faiths should have them, thus the loong build time.
I'd prefer lower maintenance (the extra tithes and donations would one hopes even out - the nobles should pay more if in a fancy shop church) than lower initial cost to keep them rare - temple domains should take the long view and if you figure it will benefit you for decades then the long pay-off is still worthwhile.
I would suggest though, that if captured by a rival faith, that a fairly chunky conversion cost should be present - while losing it should be a major kick in the teeth prestige wise.
