Comfrey's roots are quite deep, so they can reach mineral resources the more shallow rooted plants cannot access. The leaves provide those resources to the trees and other surface plants, and they thrive on it.
Being so deep, the roots also help break up hard soil (I have heavy clay) so rain can percolate down and other plants have more of a chance at thriving in the loosened soil.
I cut my comfey back several times a summer, for use as mulch/fertilizer, for medicinal use, and to keep the flowers from setting seed. My plants have rather boring flowers, even en masse, so while bees love them, don't expect a glorious show.
When they die back in the winter, they look black and unappealing. Take the opportunity to cut them way back and compost the leaves, and the stumps that remain won't look so bad.
I think the suggestions to interplant comfrey with some fruit trees are a great idea. If you're not ready to take on the maintenance of the fruit trees yet (Grow a Little Fruit Tree is a fantastic resource)( I can't remember the author), plan out where you'll want them, and don't plant comfrey too near those spots.
The way comfrey grows and spreads, I really think you'll want to plant less than half of what you're thinking. It's great around trees (not too close), and my raspberries love it, but smaller plants will probably be overtaken by it.
