For most nations you need to figure out what you would do with that 5 IC for a year instead of building a factory. Remember that a factory takes 5 years to pay for itself, and really only adds 1.5 TC for a year's worth of effort.
IC whoring makes sense early, but unless you're playing some sort of game where you're not going to fight for a long time, you should stop during the war. Maybe after you've defeated all opponents but one and have built your military completely and you're only upgrading, providing reinforcements, and maybe building supplies, would I recommend mid-late game builds of IC.