Edit: I'm beginning to believe that the requirements for spreading a cult are a bit too restrictive. Once I'd founded a cult, none of my other cities could be converted to the same cult.
I noticed that too, but I actually think it's a really cool way to approach these different "cults" as part of CiV's religion system. For religions like the two existing Theist ones, it totally makes sense that they should spread throughout all your cities. They're popular with the majority of the population, and they seem to have a straightforward set of religious laws that are universally recognized by all members of the faith. Same goes for the belief in "The Weave of Ea," in that it's plausible for an entire civilization's population to follow the basic belief of harmony in nature (note: I could be getting these religions' aims totally wrong, I'm just working with what I remember from the manual. Also I know nothing about religion or theology in general so if you want to call BS on what I'm writing you're probably right to do so).
The cults, on the other hand, are more specific. They're devoted to one or a couple of gods, and they focus on very specific aspects of nature: rivers, horses, wine, etc. It wouldn't make much sense for a city built in the middle of a desert to worship an ocean (well, it could, but not with the intimacy an ocean-based cult would. A desert city might hold the ocean as an ideal paradise, but a coastal city's population would naturally work the ocean into its religious beliefs because it permeates every aspect of their lives).
In Ea, I feel that the general Weave should be easy to spread to all of your cities, as it currently is. Cults, on the other hand, are pretty cool as city-specific "flavors" of the Weave. Depending on the location of your empire, you might have a few different cities with a few different cults. If you got lucky or were very smart with your city placement, you might get two or three cults in one city, giving you a variety of bonuses. Perhaps that could be another dimension/strategy to be considered in city placement: where can I put this city to reap the benefits of as many cults as possible?
I'd also love to eventually have the option to create a "custom" cult, which would give only one or a couple bonuses to your cities (akin to the Pantheons in G&K). I don't have much experience with playing as a Theist Civ, but it also be cool to have a limited degree of customization when founding Azzandarayasna.
About hoarding gold: in terms of direct bonuses, the only way I can think to encourage treasury building is to have a system like the Khazad in FfHII: the more gold/city, the more happiness/production you get. This is pretty basic and doesn't make much sense flavorwise, unless we're talking dwarfs. Perhaps one of the main benefits of having a stupidly large treasury comes from other people knowing you do; you could get a diplomacy boost with other civs from having a huge treasury ("We like you because you're rich and we want a piece of that" or "We're scared of you because you can hire a million mercenaries") and city states could be more friendly/scared of you).