I know not every spell should be some amazing, game-changing thing, but as it is, there's zero reason to use any spells besides Hand of Fate. Not to say that Hand of Fate should be nerfed, but every other spell pales in comparison.
Conjure Baked Goods' backfire is WAY too harsh to make it worth attempting it. Mathematically, risking losing 15 minutes of CpS for 30 minutes of CpS makes sense, but a clot, especially a 15 minute one, reduces the effects of clicks and wrinklers substantially. To fix this, I think you could either make it so that the backfire removes 15 minutes of CpS instantly (a la Ruin), or, make the +30 minutes of CpS a buff which increases your CpS by however amount to be equal to 30 minutes, to make the risk a bit more worthwhile.
Stretch Time's fine. Not amazing, but doesn't need to be changed.
Spontaneous Edifice was the main reason I was going to make this post in the first place. Requiring 100 mana just to use it is ridiculous; by the time you're able to reach 100 mana, you've got far, far better ways to obtain cookies to get buildings (namely, Hand of Fate). What's the point of burning through the vast majority of your mana to obtain ONE building (and possibly even LOSE one) when you could just as easily use Hand of Fate and get way more than enough to get a building. Not to mention, you can't get Prisms, and you can't get more than 400 of any building with it, so its usefulness is even MORE limited. I think it mostly just needs a price reduction; again, that wouldn't make it great, but it at least wouldn't be pointless to use.
Haggler's Charm and Crafty Pixies are fine (The risks are pretty heavy but not unreasonable), but I think you could serve to equal them out at being 30% of your mana, instead of 20% and 40%, respectively.
Summon Abomination is another fine one. It just doesn't stand out, but it's not really supposed to, I guess.
Diminish Ineptitude ought to be 10% of mana, if only because you already need to use another spell for it to be worth it.