Some Spontaneity to Wizards (3.5e Variant Rule)

Introduction
As we know there are two kind of casters: the spontaneous (like Sorcerers) and the ones who prepare the spells after waking up (like Wizards). I always found a little too rigid the system of the Wizard: it is far too easy being with an array of Fireballs when you actually needed Wind Wall.

This Alternate Rule tries to find a compromise without making the Wizard exactly the same of the spontaneous caster changing a little the rule that allows you to fill in an empty mind slot in 15 minutes.

Rationale: The main idea of this Variant is NOT making Wizards stronger, but giving them more chances to use those small hardly ever useful spells. For example when you did actually memorized `Nystul's Magic Aura` or `Vision?`

Mechanics
In this context `busy slot` means ready to cast another spell, not already used; and `free slot` means unused in the morning study.

Benefit: All normal rules apply, but a Wizard can also cast an unprepared spell if:

Once he is successful he readied the book. He can cast the spell (eventually applying metamagic) simply:
 * he seek and glance the spell in his book. This action behaves just like casting a level 0 somatic spell with casting time one minute (about attacks of opportunity, concentration checks and the like);
 * using-up a free slot of the spell appropriate level (or higher);
 * OR using-up a busy slot of the spell appropriate level (or higher) and a second (busy or free) slot of the spell level, one-lower or higher.

The spell book stays readied until the character decides to cast another spell, both prepared or unprepared. If the new spell is unprepared the book must be readied again; if the new spell is prepared your character puts away the book as a non action.

I used the the Wizard being the most iconic, but this Variant Rule may be applied to any prepared caster: an Archivist will seek in the prayer book; a Cleric or a Paladin will enter the mindset to ask his divinity and so go on...

Conclusion
With this Variant if it happens you actually need a rare spell, overall outside fights, you can cast it without problems.

On the other hand in a real fight this Variant rule is not unbalancing: losing 10 rounds is usually unacceptable as most fight lasts at most 3 or 4 rounds. Moreover if your character is hurt while reading the book he will need to pass a check of concentration or he will need to start over.