Reading it only for the caste verse misses what the composition is for.
It is, structurally, a hymn about sacrifice as the mechanism of creation. The gods perform a sacrifice using Purusha as the offering, and from that act everything proceeds, including, in a characteristic Vedic turn, the sacrifice itself and the verses used in it. The hymn describes the ritual as generating the components of the ritual, which is a self-referential move the Brahmana literature would spend centuries elaborating.
It also states a proportion that later Vedanta took very seriously: three quarters of Purusha is beyond, in the immortal, and one quarter is everything that exists here. That the manifest world is a fraction of what there is becomes a load-bearing idea in the Upanishads.
The hymn is recited in a great many contexts today, temple worship, the consecration of images, domestic ritual, and it is one of the most widely used Vedic texts in living practice. Its recitation in those contexts is not usually accompanied by attention to the caste verse.
Versions of the hymn also appear in the Yajur Veda and elsewhere with additional verses beyond the sixteen stanzas of the Rig Vedic text, the added material generally more explicitly theistic than the core, so a quotation attributed simply to the Rig Veda sometimes comes from a later recension not actually found there.
The Indo-European comparison is worth a word too. The dismemberment of a primordial being to make the world appears in the Norse account of Ymir and in scattered Iranian material, and comparative mythologists have treated it as a shared inheritance. The resemblance establishes a common pattern rather than a common text.