the philosophical questions raised by multiple, visually similar species being considered as one have come up before. Zebras were discovered to be 3 separate species. See "What, if anything, is a Zebra?" from 1983 http://polaris.gseis.ucla.edu/gleazer/462_readings/gould.pdf

Value isn't absolute, but a relation between the valuer and that being valued.

W.F. Lloyd, 1833, "A Lecture on the Notion of Value as Distinguished Not Only from Utility, but also from Value in Exchange".

http://socserv2.socsci.mcmaster.ca/~econ/ugcm/3ll3/lloyd/val...

There's no need to invoke philosophy here. It's pretty well accepted that an ecosystem with less biodiversity is more fragile, and from that perspective the extinction of a species is a concerning event, particularly if the extinction was accelerated by human actions. If new information indicates that a species or group of species is in much greater danger of going extinct than was previously thought, then it makes sense to prioritize conservation efforts for those species more highly.

5' tall proportional giraffe "ponies" would actually probably be a bigger hit than the full sized ones at zoos.