Getting more spells from Intelligence buffs

[Vaz]

When I prepare spells as a Wizard, I get a number of additional Spells per day.

I'm a Straight 20 Wizard, with an Intelligence of 28 for 3 additional L1's, 2 additional 2-5's, and 1 additional 6-9's.

Can I prepare and immediate cast a persisted Fox's Cunning to gain a bonus L2 and L3 spell which I then prepare?

[Mcdt2]

No.

Wizards (and other spellcasters who rely on Intelligence) affected by this spell do not gain any additional bonus spells for the increased Intelligence, but the save DCs for spells they cast while under this spell’s effect do increase.
However, this is a rule specific to this spell. It is possible there are other int boosting methods which lack this clause, but I don't know of any.

[Vaz]

Well, I used Fox's Cunning as an example. That is explicitly no, but other spells like Greater Visage of the Deity, and possibly more. Also, Headbands of Intellect I believe specify skills, but not spells per day.

[tyckspoon]

Your spell slots are activated at the end of your 8 hours of rest - at that point your spent slots become capable of storing a new spell and your un-spent slots can be exchanged for different spells if desired. Casting a spell *after* that rest period will not increase your spell allocation, as the determination of how many slots you get has already happened (you may have the *capacity* for more slots, but in order to activate them you would have to rest again.) However, if you had cast that spell before going to rest, then it would improve your spell slots accordingly.. assuming it lasted throughout your rest and preparation period and did not have a specific statement causing it to not work, like Fox's Cunning has.