Tom, it's a good question. There is some risk, but I don't like just one plant on small piece of e.g. bark. For me is not so important, to have just a some species. How does it looks, is also importance for me. Let me say, when you buy a rose, you buy also 5 or 10 not just one. It looks better.
For good luck I've never been having any problems with virus or fungi. Just louse, but they don't kill my plants.
I see, you look very carefully at my pictures. Thanks a lot, I hope you like them.