Can Rainbow Servant be combined with Versatile Spellcaster and Spontaneous Divination to cast all Cleric spells spontaneously?

Question

A ridiculous idea has occurred to me and I'm looking to verify if really works. Consider the following build:

• Wizard 5/Rainbow Servant 10 (a class from Complete Divine)
• At Wizard 5, take Spontaneous Divination from Complete Champion so that you qualify for Versatile Spellcaster from Races of the Dragon.
• Take Versatile Spellcaster at some point.
• At Rainbow Servant 10, you gain access to the entire Cleric spell list.
• Put together, Versatile Spellcaster and Rainbow Servant 10 should let a Wizard cast spontaneously from the entire Cleric spell list.

This gives me two questions, the first as a focus and the second as a supplemental:

1. Does this actually work? My first objection is that I'm not quite sure if the Wizard automatically knows all of the Cleric spells at Rainbow Servant 10. If you have to record them in your spellbook, you'll soon run out of gold.
2. If this does work, can the "powerful non-Diviner spellcaster class that can also cast spontaneously from the entire Cleric spell list" idea be done better? The term "Rainbow Warake" seems to be in my memory.

Answer 1

No, this does not work:

A 10th-level rainbow servant can learn and cast spells from the cleric list,

This grants the ability to learn the spells, but does not automatically have you learn them. The wizard still needs to scribe them in their spellbook, and a sorcerer would need to learn them, and so on. Spontaneous divination and Versatile Spellcaster both specify you need to know the spell you want, so those don’t change the equation.

The “full list” spellcasters, beguiler, dread necromancer, and warmage, are often claimed to be exceptions here, and that these classes really do get to spontaneously cast off of the entire cleric spell list. There are problems with that, however—see our dedicated Q&A on the subject.

Answer 2

Theoretically yes if you spend time and gold, up your DM

Step by step :

• Spontaneous Divination has been errata-ed by WotC : The first sentence should instead read, “You can spontaneously cast any spell you know from the divination school by sacrificing a prepared spell of equal or greater level.” You have to know the spell to cast it, but will give you the Spontaneous casting feature required for the next step.

• Versatile Spellcasting allows you to fuel a spell you know of a certain level with two spell slots one level lower. This should work, by sacrificing two spell slots of a lower rank and chaining with Spontaneous Divination.

• Rainbow Servant 10 allows you to expand the list of available spells you can choose from when you add spells to your spellbook. You do not automatically add them to your spellbook so yes, it could end costing a lot of gold (even if using Boccob's Blessed Book). You were right in you 1st point.

You end up burning two spells slots to cast one of a higher level you know. To me, that's a slightly better version of Versatile Spellcasting as it would work for Wizard, and that would work.

You are now a sorcerer, with one caster level increase due to the fact of being a wizard, with full access to cleric spells and the learning capabilities of a wizard. That's better than a Sorcerer 5 / Rainbow Servant 10 with Versatile Spellcasting.

As a DM, unsure if I would allow this :)

I will let your second point to other answers, but Ur-Priest quickly comes to mind.

Hoping that helps !