Even if they just keep an enemy from using an eco-sphere for a few turns, their contribution can be invaluable. Remember that Armored Personnel Carriers are amphibious and virtually invisible unless on land. The only real failing of the infiltrator is that its ability to take over or disable enemy units contains the game's sole concession to probabilities. There is always the chance of failure, and the chance that failure will bring discovery and disaster. The right upgrade to units can make all the difference in a long-term game and in some of the tactical scenarios we have provided with the game.
Attack adds to the damage done by a combat vehicle's weapon.
It can make a definite difference, especially if multiple upgrades are purchased. Enemy units designed to be able to absorb two or more hits suddenly start blowing up early. This can be very discomfiting. And, of course, it is absolutely necessary if the enemy has invested in armor upgrades. Range is a costly upgrade.