My youngest daughter was making up a story about zebras eating flowers the other night when it occurred to me that I haven't seen as many holes gnawed in flower petals as in leaves. Are flower petals as nutritious as leaves? My first guess is no, since there's no obvious chlorophyll, so presumably not much sugar available. On the other hand, pollen is supposed to be mostly protein, which is a plus: bees seem to like it. However, bees are designed to get at the pollen without eating the flower petals, so maybe the petals are unpalatable. Some flowers are edible as that excerpt from Edible Flowers suggests. This site notes that some can be poisonous; though it makes lots of claims about healing which I won't vouch for. The author suggests avoiding the flower internals and concentrating on the petals.

So I tentatively conclude that petals are somewhat nutritious, but designed to be unpalatable to bugs.