It's also important to keep in mind that, just because something has therapeutic potential doesn't mean the chemicals are in a concentration that's helpful - and not useless or even toxic.
That's something many people forget: Nature doesn't willingly give us something. Most phytochemicals are intended to protect the plant against being eaten.
Well, I only have basic botanical knowledge, as my degree focuses more on human - and molecular biology. But phytochemicals are generally produced to help the plant thrive, be it to avoid being eaten (most uses) or kill other plants nearby (that's not too rare either).