Heh, reading everyone's ideas together confuses the hell out of me. To those wondering whether MoM's system is balanced? I think it is, in a general sense.
To really appreciate the balance of MoM's system you have to realize the inherent tradeoffs in it. If you focused exclusively on sorcery (11 blue books) you had a very weak early game. Sure, you had a lot of different ways to counter the enemy's spells but that meant you'd spend all your time researching these instead of researching spells that actually do something. You also had to consider the possibility that your opponents' strategy might not involve a lot of buffs for you to dispel, negating the benefit of such spells.
The other big balancing factor that mitigates against a guy who "counters everything" is mana costs. In MoM's system, casting Dispel Magic (or its counterparts, Disenchant Area, Disjunction or the True versions of all 3) is never guaranteed to remove any effect. The spell itself involves a calculation based on the amount of mana you put into it
For example, if you spend 100 mana to dispel a 100 mana spell, your chance of dispelling it is:
(100/(100+100))=0.5 or 50%
If, on the other hand, you spend 200 mana, your chance to dispel it is:
(200/(100+200))=0.666 or 66.6%
Twice as much mana, not a huge increase in result. Thus you are forced to make some very tough decisions about how much mana you want to risk, how quickly can you cast it (spellcasting skill) and how urgently you need to remove the spell.
As for the idea of making every spell have another spell which is its counter? I don't know if that would fit very well in this type of game. You can't really expect a player to learn more than 10-20% of all spells in the game on any given campaign.