Exactly. Travelling every once in a while over a large distance with a huge amount of gold, with the risk of having it stolen, is interesting gameplay.
Travelling around all the time with a few tens of gold is boring !@#$.
That's why upkeep gold can be sent via NPC couriers, merchants, pilgrims, whatever. But the massive amounts required for enlarging a temple can not.
I've never found traveling great distances to be of any interest whatsoever, quite the contrary actually. And as long as you don't go in enemy lands (if your realm has any enemies at all), you are pretty much as safe as it goes for that gold of yours that you are transporting. Traveling was always considered a necessary evil, which I did reluctantly in most cases because I had to.
Furthermore, religions were tax havens, yea... but this is also what allowed to stockpile gold in order to build or enlarge temples. In most active religions, if a lord would stockpile a ton of gold for personal reasons, he'd have a high risk of seeing that gold just grabbed from under his nose by the religion leaders for other purposes. How are we going to finance these large temples, now? We are going to have their duke tax the money they are giving themselves, therefore giving them a ridiculously high balance? Much higher than what they actually gave, therefore allowing them to go in other temples to withdraw more gold than they ever actually contributed? All lords will be able to do this, but the scale at which the big cities will be able to do this is way beyond the religions' capacity to pay. It'll simply make them go bankrupt. Religions require much more massive investments than guilds do.
