While Age of Wonders & Master of Magic made spellcasters have their own manapools, we shouldn't do it like those games did something just because.
I completely disregard realism as well.
The system that should be used is the one that is best for gameplay. I trust Derek to make the right decision.
AoW2/SM had a global mana pool and global mana generation. All spell costs came out of it, as did all upkeep costs for summons and enchantments.
But it also had "casting points", which was how much mana a caster could draw from that pool in one turn. That also differentiated between a weak caster (10 points, or really just one spell), a strong caster (30 points), and the empire leader sitting in his tower with a caster's throne and caster point increasing magic item (up to 90 points). The system also supported multi-turn spells because casting something with a cost of 300 mana required 300 casting points, which took however many turns based on the caster points available.
That system worked well. I don't like "local mana" at all because it's not intuitive. If I build a shrine that generates mana, who gets it? If everyone gets it, then I'm effectively multiplying mana generation by having more casters. If it's split up, I'll wind up getting 0.1 mana per turn and it turns into population growth in WoM 1.3 all over again where you annoy the player into submission with penalties. With global mana it's easy: 2 mana is 2 mana.
As Alstein mentioned in his idea, you can limit tactical casting using casting points, or a stat like INT to duplicate the same effect (if say 10 INT = ability to draw 10 mana per turn).
