IMO, multi-classed spellcasters are fine the way they are. Their increase in versatility makes up for their lack of "boom-power" (unless one is playing in a combat-only game, in which they can add their own damn house-rules instead of inflicting it on the rest of us).
I'm not trying to pick on anyone, I just picked this quote out. It seems like this sentiment is around a lot on the boards, and it sort of bugs me.
First, a multiclassed spellcaster is not necessarily an arcane/divine multiclasser. So a Evo/Sor and a Clr/Drd are both multiclass spellcasters, in addition to the more "traditional" clr/wiz, drd/sor, what-have-you.
Second, a multiclassed spellcaster does therefore not necessarily gain much versatility.
Non-Extreme Example:
Clr5/Sor5- concentrating on dual-wielding arcane/divine magics with a minor in turning undead.
Highest Spell Level: Clr3/Sor2
Probable Highest DC: 13/14+spellcasting stat (char has 2)
Spells Per Day (both charts): 11/12/9/3
Spell Penetration: 5+d20 (for either)
"Versatility":
-Casts 9 non-Orisons (assuming 16+ Wis) and 3 domain spells
-Knows 6 non-cantrip Sor Spells
Ok, so we are talking about knowing/preparing 18 "different spells" (not including cantrips/orisons) and being able to cast a meaningful spell 24 times a day.
vs
Sor10- concentrating on whatever
Highest Spell Level: Sor5
Probable Highest DC: 16/17+spellcasting stat
Spells Per Day: 6/6/6/6/5/3
Spell Penetration: 10+d20
Versatility:
-Knows 15 non-cantrips Sor Spells
Ok, so we know 3 less psells but can cast 2 more meaningful spells a day. Not to mention we know 2 more spell levels worth of spells, which in and of itself lends greater versatility. This character can't turn undead and can't heal, but in general situations will be far more useful than the more "versatile" multiclasser.
Extreme Example:
Wiz10/Sor10- ultimate flexibility and versatility!
Highest Spell Level: Wiz5/Sor5
Probable Highest DC: 16/17+spellcasting stat
Spells Per Day (both): 10/14/12/11/10/7
Spell Penetration: 10+d20 (for either)
Versatility:
-Knows 15 non-cantrip Sor Spells
-Preprares 22 non-cantrip Wiz Spells
Alright, this is a 20th level character. I'm assuming they managed to swing a 22 in each spellcasting stat via items or what-not. We're looking at about 37 unique (non-cantrip) spells per day, give or take and none are higher than 5th level. Total Castings: 54
Sor20
Highest Spell Level: Sor9
Probable Highest DC: 20+spellcasting stat
Spells Per Day: 6/8/8/7/7/7/7/7/6/6
Spell Penetration: 20+d20
Versatility:
-knows 34 non-cantrip Sor Spells
Ok once again we are down 3 spell in the unique (non-cantrip) spells per day but with higher level spells comes more versatility/flexibility (inherently). Total Castings: 63 (with a primary stat of 24).
I think its clear that in a basic example a dual caster is behind the curve, and in an extreme example they are not even in the ballpark with a straight caster.
Technik