@hue-man,
Perspectivalism need not claim that every perspective is equally correct, and my reading of N. does not suggest that he himselft understood them to be of equal value or worth. Danto, in discussing this, takes the position that, for example, a perspective that takes into account both other perspectives as well as includes more "data" is superior to a more narrow or limited one.
Nor does perspectivalism force upon its adherent the position that there is no "objective" reality; it does seem to imply that our knowledge of it, however, is perspectival in nature. One could draw an analogy with the Kantian position that noumena are in themselves unknowable because they must be conditioned through transcendental filters to be knowable, and that we cannot go beyond these filters to determine if anything corresponds to that which is filtered.
Nor do I think perspectivalism (or for that matter N's philosophy taken as a whole) contributes nothing to the field of philosophy. First, it reminds the philosopher that other perspectives are possible and encourages him to look for them rather than assume his positions are absolutely correct. Second, it opens up new methods of analysis, and suggests the study of how different perspectives have grown and interacted. Schultz, for example, has investigated both perspectives and "horizons" in his philosophy with subtlety and penetration.
Regards,
John