So, here's what's with staffs:
Advantages:
- User's casting stat affects save DC
- User's caster level affects variable aspects of spells/overcoming SR
- Higher level spells
- Variety of effects
Disadvantages:
- Expensive
So, an ideal staff would take advantage of the good aspects of staffs, but tries to minimize the expense.
Here's a not so good staff:
Charming: Made of twisting wood ornately shaped and carved, this staff allows use of the following spells:
Charm person (1 charge)
Charm monster (2 charges)
Moderate enchantment; CL 8th; Craft Staff, charm person, charm monster; Price 16,500 gp.
This staff gets you some combination of 25 uses of Charm Monster (a 4th level spell) and 50 uses of Charm Person (a 1st level spell)
By comparison, a Wand of Charm Monster gets you 50 uses of it for 21,000 gp. That's 100% more uses for about 25% more gold.
This staff doesn't have high-level spells. Also, an arcane spell caster with Charm Monster on his list is very likely to prepare it/have it to begin with. So it doesn't really add variety. (The higher spell DC is nice, though.)
Here's a better staff:
Abjuration: Usually carved from the heartwood of an ancient oak or other large tree, this staff allows use of the following spells:
Shield (1 charge)
Resist energy (1 charge)
Dispel magic (1 charge)
Lesser globe of invulnerability (2 charges)
Dismissal (2 charges)
Repulsion (3 charges)
Strong abjuration; CL 13th; Craft Staff, dismissal, dispel magic, lesser globe of invulnerability, resist energy, repulsion, shield; Price 65,000 gp.
This has a variety of spells on it, that the caster might not necessarily carry with him: Repulsion sometimes gives you tactical control of the battlefield, but is not so useful when, say, attacking an entrenched enemy. Dismissal is effectively "save or die" for extraplanar enemies, but not so good in other circumstances. Lesser globe of invulnerability is great against groups of lesser spellcasters, but not so great against high-level spellcasters. Resist energy also has situational uses.
The spells in this staff add variety to the user's repertoire, that might not otherwise be present. Also, some of these spells are level-dependant enough that you'd rather have a staff than a stack of scrolls: Resist energy's bump to 30 points at Level 11, Dispel Magic's level check, and Dismissal's special saving throw.
Still, I think all of the staffs in the DMG could stand a little improvement. A have a few ideas for staffs that take advantage of the 3.5 rules, rather than being hold-overs from earlier versions of the game.