I think one's motivations to request multiple samples would primarily be based on one's field of interest. Selections "b" and "d" would probably be important to a science historian or to an archaeologist (and "d" perhaps also to a process engineer), whereas those selections hold no interest to someone like me. Someone working on a specific museum-represented locality (or who thinks a specific museum-represented locality might be a good analog for the more obscure locality they're studying) might be very interested in selection "a". A person working at a Cu mine might be interested in how different Cu minerals might react to an ore treatment process, and so would be interested in museum-characterized examples of Cu minerals (selection "c").

To quantify the relative importance of selections "a" through "f", one might need to know the relative proportions of the professionals (mineralogists/petrologists; metallurgists, chemical engineers, artists, archaeologists, etc.) that might want to use museum samples, and also their relative familiarity with knowing museums actually can loan out specimens for study. Regarding the latter point, quite a number of my students were surprised to learn that they could potentially augment their self-collected or purchased research specimens with museum samples; to them, museums were just passive storage facilities with interesting displays.