Dissipation Field (upgraded) is actually better than Dissipation Shield (non-upgraded) because the Shield takes Entropy quanta from you based on each attack...so a 1-damage creature will suck 1 quantum from you, just like a 3-damage creature will. In effect, this turns all 1-damage creatures into 3-damage creatures as far as your Dissipation Shield is concerned. It turns 4-damage creatures into 6-damage creatures, and so on and so forth.
However, the Field drains only the amount of quanta that the creature actually does. Also, since Quantum Towers churn out 3x the amount of quanta, it doesn't matter that 3 damage creatures are draining 3 quanta instead of 1. So basically, even though this is an Entropy-related shield, it's much more useful for a Rainbow deck.
Example: Diss Shield with 10 Amethyst towers vs. 10 Elite Skeletons, starting with 50 quanta:
Round 1: -20 quanta, regenerate 10 (40)
Round 2: -20 quanta, regenerate 10 (30)
Round 3: -20 quanta, regenerate 10 (20)
Round 4: -20 quanta, shield dies.
Example: Diss Field with 10 Quantum Towers vs. 10 Elite Skeletons, starting with 50 generic quanta:
Round 1: -20 quanta, regenerate 30 (60)
Round 2: -20 quanta, regenerate 30 (70)
And you keep going up, up, up.
I think the only time a Dissipation Shield matches a Dissipation Field is if your opponent is using only creatures that have an attack rating that is some multiple of three.
