For the worldspell, I rarely use it. Maybe if I face like the sheim or the balsferas, and they're actually summoning things (aka, not likely) or I have a bunch of mana nodes and some casters who could use the xp (again, rarely happens).
For religion, my favorite religion is OO for one reason - hemah. With OO, I get 2 archmage hero's, bringing my total number of channeling 3 casters (after govornnan teaches the others) up to 18. On top of that, it gives you stygan guards who are excelent for overseas attacks - rather than worrying about ships, you can get some firebows with water 2, stygan guards with water walking, and then your mage army with all your artillery. If I cant get OO (or am playing orbis, where it would turn me to evil), I would probably go with either RoK or Empyrian (again, probably wouldn't choose empy in orbis as it turns to good). RoK to help pay for upgrading all those mages, Empyrian for chalid (another powerful channeling 3 caster, plus very powerful extra spell for the high priests).
As for the influence that the leader traits have, there are some pretty big ones.
Generally when playing as Valledia (organized, arcane), i tend to focus a bit more on the other aspects of the amurites - the firebows, the everyone can cast haste/whatever other spells I have with the mages functioning more as support. Much of it revolves around running theocracy/apprenticeship/conquest + getting form of the titan and building command posts everywhere. The whole goal is to start with as much XP as possible for my firebows and such so that the firebow can grab stoneskin+drill 1-2 for attacking, or fireball+stoneskin+water walking for mobile offense, or fireball+stoneskin+regeneration as a kind of medic, or stoneskin+hope+fire arrows or something else city boosting as garrison troops.
Playing as Dain, I tend to focus more on the mages. Running aristocracy/agrarianism, and caste system (apprenticeship till I get caste system), I focus on running as many scientists as possible, with the goal being to get them and pop my way up the arcane line as fast as possible. I tend not to actually research the arcane line if I can help it, preferring to go for the priest line to unlock them faster while I bulb my way through the mage line. The big exception is sorcery, which I prioritize getting. Once I have sorcery, then I can spam wizards who come out with plenty of xp due to the cave of the ancestors. I then use wizards for boosting my cities, and for my offensive stack, while having somewhat weaker units defending my cities and my wizards (swordsmen, archers - if following OO I'll defend with stygan guard). Here I focus on wizards and the summoners alot more than when playing as Valledia, but focus significantly less on the support units like the firebows.
Lastly, for Mana Nodes, I prioritize getting an earth node because stoneskin is VERY helpful for keeping mages alive, and allows firebows to do something useful. I also try to get an enchantment node for at least long enough to get a few wizards with enchant, for buffing melee units and archers. Further Mana nodes will vary according to which leader I'm playing as.
With Valledia, I tend to focus more on specific nodes to buff my casters, and it tends to build off either fire mana (which the palace provides) or the mana from whichever religion I'm following, or if I have a mana providing UF. So if I start near the mirror of heaven, I'll tend to buff sun, and go empyrian. Or if I go OO I'll tend to buff water. If I'm unable to get the holy building, I'll generally fall back to buffing fire or death.
Playing as Dain, much of my power lies with getting wizards asap. So I'll try to get 1 of each mana node, though I may focus a little on one or another node if I need something. If I have enough nodes to make it worthwhile, I'll occassionally even go through an adept building spree with as many different mana nodes as possible to maximize starting xp, then wait to upgrade them until I focus on a few different mana types to give them free spells while my cities build something else. I'll always try to focus on a few mana types when upgrading to archmages or building hemah. Govornan, I'll tend to try to pair up nodes to allow him to teach as many lvl 1 spells as possible. Once he has as many level 1 spells as I find useful, then I'll send him down to teir 3 of whatever path I'm buffing (if I have enough nodes, then metamagic, if I don't then I'll go down fire, death, or sun).
Hope this helps. Sadly, as powerful as they can be when used well, it does require a good bit of micromanagement, and even then has trouble matching other civs unique effects. The only time when they really shine is once they have at a minimum 4 mana nodes. Once they start getting more than that, then they can start really rolling along. However mana nodes are generally rare enough that that is near impossible to get.
-Colin