What is your opinion of specialist mages with ToTL installed?

Do the opposing schools make the benefit of an extra spell per level not worth it?

I was thinking of playing with an Illusionist and a Bard as a backup spellcaster. The idea is that the Illusionist can memorize all 9th level spells in this game, while a Bard can learn any spell up to 8th level to cover the Abjuration (Dispel Magic) and Necromancy (Skull Trap, Horrid Wilting) spells my main Mage would miss out on.

<font color = lightgreen>No, having one extra spell slot per level is not worth the loss of entire schools of spells. Specializing is never worth it. </font>

I chose a specialist with the bard sometimes...but sometimes I don't.

I hate losing some of the abjuration spells with the illusionist. The spells that hurt the most to lose are the Globe of Invulnerability spells and (especially) Mind Blank. The bard can do the necromantic work [although you do lose the only 7th level single character attack spell: Finger of Death], but that abjuration loss is the stinger. That 9th level summon spell doesn't impress me as much as it should...casting Shades and getting a Troll walks all over the 9th level summon spell!

Wee hint:
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There is a certain dagger the illusionist can use to make up for the loss of the Antimagic Shell though.

Current HoF party [going b*lls to the wall -- a pain at start, but killer now]:
Human Paladin
Dwarf Fighter
Gnome Fighter/Cleric
Half-Elf Fighter/Druid
Elf Fighter/Mage/Thief
Half-Elf Bard

I'm finally giving up on a SC druid for a MC druid for a better RoF slinger...I plan to get the priests to 19 strengths each -- allowing for more defense for the tanks {since they are tanks...after all} and wicked sling power for the priests : )

I'd say it's generally not worth going the specialist route, because if you have only one or two arcane casters, versatility is more important than specialization.

Doing the illusionist & bard thing is ok, but you have to be aware that it leaves you with slightly limited arcane options.

A situation where I would definitely consider using a specialist is in cases where you have more than two arcane casters - however, three arcane casters requires lots of planning as to who gets what. With dual and multi-classing, there's plenty of room for three arcane casters. I could definitely see a party with a bard, d/c or mc fighter/mage, and dc or m/c thief/illusionist, for example. The bard mostly casts buffs, F/M takes battle magics, especially touch spells and "spray" spells (Cone of Cold, Prismatic Spray, Burning Hands, Color Spray), and T/I is a straight bomber, minus necromancy spells.

What about the 2 schools cancelling each other out?

I don't mind taking a nice gnome thief/illusionist backing up a non-specialist wizzy.

However, I'm not too keen on going the specialist route with my primary wizzy. I don't find that the extra spell per level is worth the cost.

Two schools "cancelling" each other out (e.g. illusionist and necromancer) is fine, but you still end up with situations in which only one character can cast certain spells - it's ok as long as you are prepared for it, but things can get messy if the key mage is busy or affected by spells when you need a particular spell. I notice this most when dealing with mental effects (fear, sleep, stun) in the Tiers of the Dead, against wailing virgins in HoW, and in TotL against harpies and jackalweres. If taking two specialists, be sure to have at least one cleric in the party to help against mind-affecting spells.

I wouldn't take two pureclass casters on principle, but a necro as a bomber and a fighter/illusionist as a supertank would work fine.