I agree that resource spawning spells are not necessary. They are very flavourful but encourages micromanaging, there are already lots of resources in Orbis and I'm not sure if AI can use those spells. What's more it gives two guilds more power as they can increase amount of resources they use without war or trading. Maybe Prospectors and Three Fields unique building can increase chance to spawn (or maybe spread in case of Three Fields) resources passively a little, like Earth mana do, but I have no idea if it's easy enough to code. You can always keep them for now as you have little time and change them in later patch if you like.
I did some math about income generated from resources with guilds. I used numbers from BTS, assuming that those numbers are balances after all those pathes and playtesing BTS got. I also assumed that amount of resources civ can get is similar to amount in BTS which may or may not be true

As I suspected, BTS designers decided that food is most valuable in game, followed by production, gold and science and culture. None of BTS corporations gives commerce, but I think it should be valued as gold and science (a little bit higher probably but very little). In BTS all but one corporation uses between 3 and 5 resources and amount of resources used doesn't seem to affect benefits. One civ uses only one resource and it gives 50% more benefits then expected.
Aluminium: Uses 1 resource, gives 3 science and 1 useful resource.
Cereal: uses 3 resources, gives 0.75 food each
Jewlers: uses 3 resources, gives 1 gold 4 culture each
Construct: uses 5 resources, gives 0.5 prod and 3 culture each
Mining uses 5 resources, gives 1 production
Sushi uses 4 resources, gives 0.5 food and 2 culture
Ethanol uses 3 resources, gives 2 science and 1 useful resource.
Food is worth about 0.75 per resource.
Science and Gold are worth about 2 per resource.
Production is worth about 1 per resource.
Culture is worth about 3 per resource.
Bank of Vivaldi: uses 2 resources, gives 2.5 gold. A little bit higher then expected but is uses only two resources so it's ok.
Circle of Eight: uses 5 resources, gives 2.5 science. Probably should be just 2 science as other benefits (2 free xp, free promo, unique unit) are very good.
Globe Troupe: uses 3 resources, gives 0.5 gold and 1 culture. It needs major boost IMHO - 1 gold and 3 culture should be ok, 0.5 gold and 5 culture would be even better. BTS Corporation is somewhere in between, giving 1 gold and 4 culture. Alternativly, they might have 3 culture and 3 espionage.
Circle of Transmuters: uses 5 resources, gives 2 science. Seems ok.
Hansa: uses 5 resources, gives 0.25 food, 1 gold. Might need a little boost - 0.25 food and 1.25 gold, but nothing major.
Intricate Weavers: uses 4 resources, gives 0.75 commerce, 0.25 gold, generates 1 resource. Also a little too low, doubling it should be more balanced with 1.5 commerce and 0.5 gold.
Order of Archos: uses 3 resources, gives 0.75 production, 1 science and 0.25 culture. A little nerf might be needed here - while science bonus might fit guild flavor, we already have to 'science' guilds so you might want to remove it and increase culture a bit (to 0.75, it's 25% of 3 so fits perfectly)
Prospector's Guild: uses 4 resources, gives 1.25 production and 0.5 gold, generates 1 resource. I would nerf it to 1 production only. Bank of Vivaldi, Globe Troupe and Hansa are already giving gold so leave gold for them.
Three Field Order: uses 5 resources, gives 0.75 food and 0.5 gold. Same thing - food is even more valuable in Orbis, so I would remove gold from this Guild.
Guild: uses 2 resources, gives 1.5 gold. This one is strange

I'm not sure if it should be a guild even, but if it is, 2.5 gold per resource would be more balanced.
Of course, it assumes that all other guild aspects (like buildings and special abilites) are balanced but I believe they should be balanced with each other, not interfering with benefits per resource.
Also, two corporations in BTS are generating useful, late game strategical resources. It is very useful mechanic, as you can try to get guild if you don't have those resources. In Orbis terms, mithril and reagents should be generated by Prospector's Guild and Circle of Eight. This can be done by national wonder (that required 4 of guild unique buildings) providing mithril or reagents. It can also be done with Silk and Weavers guild.
Speaking of buildings:
Bank of Vivaldi:
1. Vivaldi Branch (+2 gold, +10% gold or +2% commerce per Guild present). New version is intresting but I think it should be gold, not commerce. It's not that important because in Civ4 gold, science and commerce bonuses can easily be changed to each other.
2. Banker spreads Gulid and can Oversee Trade (+5% commerce, free merchant). I'm not really sure, it's intresting because it forces you to choose between spreading guild and giving your cities a bonus but increases micromanaging. Free merchant is very powerful - one merchant slot might be better.
Circle of Eight:
1. No unique building, but 2 free XP and nice free promo. Maybe it should be done with building, just to make it more in line with other guilds.
2. Magister, unique arcane units, very nice. Starts with Metamagic I and II but can only build Metamagic, Enchentment and Mind nodes, so it's not better than adept, just different. Discover Technology is nice, but leaving it to Alchemist might be considered.
Globe Troupe:
1. +20% culture is nice. Guild is not very powerful so it's building can use a little boost (like +10%) in espionage or gold.
2. Thespian with it's Great Work (for 45 culture) is nice, but weaker than Banker or Magister. Maybe they can use Loki's Entertain ability (probably a weaker one, with 1 gold per 3 population)
Circle of Transmuters:
1. Alchemy Lab. Very powerful building I don't really like. It makes Alchemy tech useless to anyone but Mechanos unless you manage to get Circle of Transmuters. I think Alchemy Lab should be normal building with Circle only addon Expanded Laboratory that gives +10%. In exchange, Alchemist unit would get a boost.
2. Alchemist unit is not very powerful or intresting. Maybe ability to sacrifice it (attach it like a great general) to give one of your unit Healing Salve (one time version) or Alchemist II promo to Spy unit. They can also Discover Technology better.
Hansa:
1. Custom House is nice, but late building so adding +2 XP to water units and nice promo from guild to it might not be wise. Maybe move Custom House to Compass ?
2. Trader. Rather weak one, can use a boost. Since it becomes aviaviable at same tech as Cogs/Holks, maybe it could be sacrificed to add Daring promo to naval units ? Also, might start with Sentry I to represent Trader's ability to see oportunity (like more resources ;>) when they arrive.
Intricate Weavers:
1. No building ? Maybe a little altered Tailor would fit here as it's removed from Kuriotates ?
2. Weaver is nice. As with Oversee Trade, I'm not sure if free Bard is not too much.
Order of Archos:
1. Cathedral is ok, might give +happiness with State Religion
2. Architect. Ability to hurry building is very useful. Is it always half of units cost or you can make Architect better at hurring building than Soldier of Kilmorpth.
Prospector's Guild:
1. Miner's Camp. Nice, but I'm not sure if +1 gold is neccesary.
2. I wrote about spell before. If you decide not to keep it, something connected with production would be needed - maybe ability something giving short term boost to production but also some unhealthiness or giving production for every resource in city radious.
Three Field Order:
1. Werehouse. Same thing as above, I'm not sure if +1 gold is neccesary.
2. Farmer. Also, same thing as above - if you're not keeping it, some food based ability would be needed.