Plants are indeed a rich source of many metabolites and peptides that can offer solution to many biomedical problems. I mean they have done that in the past. To name the most famous ones take example of metformin (the top diabetic drug) and aspirin. Leads for both these drugs were isolated from plants. It is a different thing that we can make most of it synthetically now, the point being that the plants have so much to offer. And that is also the main reason why we should be concerned about preserving the biodiversity of plants, like you mention in the end - you never know what other invasive plants have to offer.