We started with plants that attract beneficial insects, but I'm with you on composting plants too. I have some comfrey started and it's been growing this summer but it's not going to be in full force until next year. The real way to spread comfrey is to grow it in a smart pot and let the roots grow through the pot, pull the plant, and let the new plant form. FYI, comfrey spreads through it's roots and not seed. So, if you hit a comfrey plant with a rototiller, then you are going to have a huge mess of comfrey. Some people thought that they were killing the plant, but they just really helped it spread. So, it's an intrusive species and make sure that you have it planted where you want it to be FOREVER lol...
The reason to compost these plants is that they are high in iron and it will counteract the high phosphorus in most compost. I've been having my compost tested for a while and it's always super high in P and very low in Mn(not Mg). I started using greensand(Mn,Fe) in my compost and it's been working great.
I'm going to compost comfrey and make KNF inputs called Fermented Plant Juice(FPJ) and it's some of the best stuff that I have worked with! You get the enzymes, vitamins, and auxins that you miss out by composting. It's like a blood transfusion for plants. Plant vampirism lol... You are using brown sugar to suck the juice(blood) out of the plants through osmosis.