Do ability enhancing items (such as the headband of
intellect, cloak of charisma, and periapt of wisdom) grant
bonus spells to the appropriate spellcasters? The spells
these items are based on would seem to prohibit it, but the
only things specifically addressed in the item descriptions
are skill points.
Yes, you can get extra bonus spells if you have an item that
increases the ability score that governs your spellcasting. To
get the extra bonus spells, you must wear the item while resting
to regain spells and all through your initial daily preparations
for spellcasting. (Even characters who don’t prepare spells need
to meditate a little while at the beginning of the day; see Daily
Readying of spells under the Sorcerers and bards section of
Chapter 10 in the PH.)
If you lose the item, you immediately lose the bonus spell
slots the item gave you, starting with any uncast spells you
have of the appropriate levels.
