telfer , page-6

Yes, people are more excited by the presence of heavy REEs because more rare and valuable among "valuable earths anyway, including light REEs"

Key points to consider (among others) are
. the size of the resource
. the proportion of heavy to light REEs
. the presence or absence of uranium (complication in some cases, positive interaction in others)
. the ability to mine and ship
. the ability to value-add by processing into customer-specified REE parcels (e.g. Lynas)