I know that whipped cream also has air incorporated into it, so it can actually be used as a leavening agent. But compared to whipped egg whites, is the leavening power more or less (or maybe even the same)? And with something like an angel food cake, would the whipped cream work as a substitute? Thanks!
It would not work. The benefit of egg is that it is largely (aside from water) comprised of protein (~12g/100g). This forms a stable structure when you whip it, that is maintained because the proteins denature (that's why the white goes white from clear when cooked) and form an insoluble and highly stable mass.
Cream, on the other hand is largely fat (19g/100g), which forms an emulsion when whipped. When you heat fat - it melts. This would mean that the batter would lose its air and structure.