I absolutely love this concept! I don't quarantine my fish either, mostly because I don't have the time or space for more worry and tanks. I did however medicate my tank once when my betta fish and tetras got ich. I separated the snails and dwarf frog I had and I guess I must have put them in too soon; my frog sadly passed away. I also like the idea you mentioned of seeding your aquariums with biologically active things. That is exactly what I do and I adore looking for my potentially "bad" animals like majano, crabs, bristle worms, etc.