In isolation it's hard to distinguish. But if you find 30-50 reactors all over the globe that were all critical at the same time and all went silent at the same time, I think you'd have to think very hard about how that happened.

As for 1) current proposals (which continually fail to be implemented) are actually to concentrate the stuff and put it in geologically stable locations (c.f. Yucca Mountain). That would seem to be easier to find.

And 2) isn't really plausible. You can't select out and "convert" isotopes like that. You get the fission products you get, and your choice to get "more" out of them is really about how long you are willing to wait for them to decay.