I've loved this thread actually, it makes me very glad we put in the Thaum Houserules and Rules of Thumb we did for Dallas (basically a thematic nerf). Our house rules design focused on the Powering Phase.... and then retroactively worried about the Declarations Phase afterwards.
I know with Houserules, everyone has their own preferences, but ours have bene worked out / tested over 2+ years of play and we're very happy with them. The only reason I bother to post them is because I think it might be directly relevant to the OP's question and this discussion.
For the curious - a high level summary of our House Rules/Rules of Thumb.
Phase 2 - Spell Preparation/Meeting Complexity0) The Given - The GM is responsible for making sure any Declaration is Thematically Appropriate
1) Declarations have to be thematically unique as well as capped to one Skill/one character contributing it. (I.e. for the casting of a single spell, only one character gets to claim a Resources Declaration: "High Quality Spell Components" - if an Assistant also wants to lend a Resources Declaration it has to be different, like "Upgraded Your Lab With Better Trappings")
2) All Declarations from a single character are slaved to the Time Increment table on page 315 starting with the "No Prep" Complexity value at "Instant" and the first Declaration at "A Few Moments." Declarations from Assistants happen in parallel and don't add additional increments. Time Increments determined from the Character with the most declarations (usually the caster). If the character needs fewer Time Increments than what this system determines - Fate Points required, 1 per reduction. Any skipped scenes or "extra time" is added after the base Time Increments is determined. Invokes and Sacrificed Consequences usually add no Time Increments.
3) Total number of "Assistants" that can add Declarations/Consequences is limited by the caster's skill level in a handful of skills (i.e. skill cap) - we use Rapport (how charming you are), Lore (you know the magical rules of using more folks effectively) or Discipline (you're just organized enough to run with a group of helpers).
Phase 3 - Casting/Powering the Spell1) Exchanges slaved to the Time Increments table on pg. 315 starting at Exchange 1 with "A Minute." To take Fewer Time Increments requires Fate Points. Adding Additional Time is not applicable during Powering Phase. This only applies if the Spellcaster claims "Unhurried" / "Doing it in Downtime" - if the Spellcaster is willing to make Control rolls in-scene/during game (subject to GM compels and in-scene complications and interference), then each Exchange is "A Few Moments" but still limited by #2 below.
2) Caster limited to Discipline (how long he/she can focus) in Exchanges. Anything more requires Invoking an Aspect to gain an additional Exchange.
3) Any sacrificed Consequences for power, assistants lending power (Assistants must come from same group and limits determined during the Prep Phase), power boosts for Environment, power taken from objects that store power, or power provided by deals with Outsiders must specify which Exchange the "whatever" bonus is gained (this list of power sources taken from page 248 "Other Power Sources")
We found that by basically "capping" the Powering Phase and slaving it thematically to the Time Increments table... the rest takes care of itself. Yes, absurdly high Complexity spells are still possible (there's an evil fae in our campaign who kills 3 humans during the course of her highest forms of magic, with 2 assistants, that hits 75 Complexity)... but it's very, very easy for us to "Tell The Story of the Spell" now. We know *exactly* what the spell "looks like" due to the uniqueness requirement of the declarations.
(for example, the evil fae above, I can describe exactly how she does her spell, what it looks like - the description of each declaration - and how long it takes - a week for the prep phase - including kidnapping and torturing the victims, half an hour for the actual powering - including the actual slaying - which means I can also as GM exactly describe the effects in the campaign whenever she starts up one of her big spells and give clues to the PCs of what's going on .... kinda like in Storm Front - Harry vs Victor Sells. So long as I gain "Story" ... I'll put up with big numbers.)
Your table's mileage may vary
Money where my mouth is - Recently I took our house rules, worked up a spell, then wrote a piece of fiction based on a single spell so that I could visualize an implementation of "Norse Magic" I wanted to put in the hands of a handful of our NPCs (including some Norse themed bad guy Fae). So, using the declarations and time increments we worked up by the formula of our house rules, I actually set the scene. Basically... my "GM Notebook" exploded into crappy fan-fic.
If you don't speak Irish the story title is simply "The Story of the Spell" (
brón orm, ach b'fhearr liom an Ghaeilge )
http://www.obsidianportal.com/campaign/dfd/adventure-log/an-sc-al-ar-an-t-ortha