I'm not talking about illegally casting a spell at all. I'm only talking about preparing a spell to say: "hey I might cast something with this familiar or spawnpoint" and then never actually using it because it is not legal to do so.
The response I got was not really directed at this concept, but rather at the concept of illegally casting spells which I assumed was right out. Seeking Dispel can only target an enchantment which has been cast but not revealed: This does not apply to what I said. Similarly the binding of a spell to a wand example does not apply to what I was saying as it is clearly illegal: it is not a suitable spell to be bound.
Using a couple of examples: The text of Goblin Builder says: "Can cast only Corporeal conjurations which are not attached to an object..." It does not mention what he can prepare. The text of Lair says "During the Deployment Phase, Lair may summon 1 animal creature." The key word summon here implies casting a spell, it does not refer to preparing a spell that one does not intend to cast. The bluff entry does create some confusion with this.
After re-reading the entries of the Familiar and Spawnpoint it is clear that attached spells would be revealed upon death (which seems like sort an irrelevant point if what you are doing isn't illegal), and it is clear enough in the case of the familiar that you are only supposed to select spells which your familiar is eligible to cast, however the text of the Spawnpoint does not make this completely clear even on close reading. You may want to reword it to more closely match the familiar wording. The bluff entry could probably use the words: "due to a lack of mana or legal targets" added to it as well, just to make things more obvious.