I have trouble believing that the standard sorcerer is so underpowered. This new one has d6 hd instead of d4, 4 skill points per level instead of 2, an extra spell known at each spell level (albeit from a list of related spells), and special abilities (generally at least equivalent to a feat) every 3 levels, compared to a wizard's bonus feat every 5 levels... Ah well, perhaps my intuition deceives me. Sounds like your group is having a good time with your alt-sorc, and that's the important thing.
Regarding energy opposites: I agree that acid is the opposite of electricity, but I get there by a different route:
In my own system, each element is associated with two energies. Cold is associated with water, of course, and most acids are liquid; fire is obviously fire, and electricity, in the form of lightning, is similar to fire, but manifested in air. Lightning and thunder are neighbors, so electricity is close to sonic. Sonic is air when it vibrates, and force is air when it remains immobile. The arc from water to fire I call the "energy rainbow," which excludes earth energies.
The two energies of water cancel the two energies of fire, and since fire/cold are opposites, that means that electricity/acid are opposites. I make the two energies of air opposite to each other, though, not opposite to the earth energies.
The "earth energies" are negative and positive energy. The negative energy is on the dark side of the rainbow (cold and acid) while the positive energy is on the bright side (fire and electricity). Death and decay is associated with the earth, but so is growth and rebirth.
In the following crude diagram, each energy on the left is paired with an opposite form of energy on the right.
...................................AIR..........................
..................................................................
......W....................force - sonic.....................F
......A...........................................................I
......T................acid................electricity........R
......E............... cold...................fire..............E
......R...........................................................
..........................negative - positive................
.............................energy...energy..................
....................................................................
..................................EARTH..........................