[CFM]

Hi Sonny.

1.
After Dynaheir casts a spell, look in her spellbook. The casted spell's icon will appear faded in it's slot, indicating the spell in that slot has been cast. As you've seen, resting will "revive" any "faded icon" spells slots.

But if you click a "faded icon" spell slot before resting, then the spell icon will dissapear, leaving an empty spell slot. You can then click a spell icon from Dynaheir's master list of known spells (the other side of the spellbook screen) to populate the empty slot.

So, if Dynaheir can cast three level-2 spells, you could empty all three of her level-2 slots, click the Web spell icon three times (on the master-list side of the screen), and rest... and she would then have three Webs memorized and ready to cast.

And of course, the amount of spells a spellcaster can memorize (and when they can memorize, say, level-3 spells) is based on the character's level. Check the manual for each classes' Spell Casting Progression table.

2.
A wand's value to a merchant will depreciate as the remaining charges decrease. The rate of depreciation depends on one or more of the following: your party's reputation score, your (leader's?) Charisma score, the type of wand, the particular merchant, ...stuff like that. When a merchant will buy a wand for only 1 gold, then that wand has only one charge left.

Side note: in BG2, there is a little number in the corner of the wand's icon (when viewed from the main game screen, after the item is placed in a quick item slot in inventory), indicating the amount of charges remaining. A small but very nice game-engine enhancement!