I never liked the fact that you can roll Spellcraft to identify a spell being cast by another spellcaster. It’s boring and doesn’t make much sense to me (yeah, that’s a hazy argument). For example: how in the Nine Hells does an ice witch from the North know what is a fireball spell? Ok, you can argue that fireball is a classic, but only from a gamer perspective. I prefer to let the player discover only some aspects/components of a spell with a successful Spellcraft check: things like descriptors, area and/or damage. Usually higher rolled numbers give more information. Of course, it easier to just say “he’s casting a fireball”, but it also removes some of the unpredictability aspect of magic (besides, “predictable magic” is something total contradictory for me).
Another reason why I prefer that approach is that I love to tinker with spells, creating all kind of bizarre variants. This is an advice given by Monte Cook in the Dungeon Master Guide 3.0 (still the best DMG for me, maybe losing only for the famous AD&D 1st DMG). Changing visual elements is easy, but I really like to make small variants.
A few examples with 2 classic dweomers (none playtested!):
Magic Missiles variants:
Holme’s forceful missiles – Each missile deals 1d6+1 damage, but the caster must roll to hit (ranged touch attack).
Valuriel’s fey darts – The caster must also roll to hit (ranged touch attack) but each target hit is covered in fey mists, suffering 20% miss to every attack roll made for a number of rounds equal to the inflicted damage. The mists can be dispersed only through dispel magic or if the target is drenched.
Damazar’s merciful infliction – The missiles do nonlethal damage and the targets are dazed for 1d4 rounds.
Baelorn’s fireball – shots a green fireball sphere that deals no damage to vegetal matter (and plant creatures), besides healing oozes. It’s reputedly an elven-version of the famous dweomer, the ooze bit being an unforeseen side-effect.
Arcturus’s unearthly fireball – shots a sphere of ulfire. Besides the usual fire damage, targets suffer 1d6 Wisdom damage (Will negates). The caster suffers 1d6 Wisdom damage himself for each casting (no save).
Blackfire – shots a sphere of black flames that deals 1d4 points of (untyped) damage per caster level (maximum 10d4). In the following rounds, all damaged targets must succeed at a Will saving throw or suffer 1d4 points of damage. This damage is continual until a successful save is made. Black flames can’t be naturally extinguished (treat it as a curse effect), but only affects creatures vulnerable to negative energy. The caster’s hands get black after casting blackfire and he ignores the next 25 points of healed damage cast on him (once this happens, his hands get back to normal; treat it is a curse).
Ancalagon’s dragonfire – Only a dispel magic removes fires started by this dweomer. It also ignores the hardness of stone, wood or iron objects. However, the caster suffers 1d8 Dexterity damage (no save) after casting it, as his hands are horribly and preternaturally burned.