Just dipping into this book, haven't given it my full attention yet, but I think you're right that the prose, in English at least, is more interesting than the poetry. Strange that he sort of talked himself out of writing poetry by his own brilliant insights into the poetic mind (especially Mallarmé it seems, who I've yet to read).
Still think cemetery by the sea is incredible, but looks like all the English translations of his poems, while impressive in places, make him read like Wordsworth or someone, which isn't quite right, (although there probably are some similarities between the two). I like the Spanish translations I've seen better mainly for that reason.