I rarely pillage. I'm an expansionist, and thus usually plan to take the cities I conquer, and don't want to have to rebuild everything. Thus, I usually limit my pillaging to key resources such as copper, iron, or a luxury. If I can take the city within a turn or two, I won't even bother with that. I actually bomb more in the Modern Age than I pillage, even if I don't get any money, because I can destroy enemy cities that I otherwise couldn't touch for a dozen turns.