I agree that it's worth the risk, but apparently Harry doesn't.

'"I thought..." Hermione said. She sounded uncertain. "I thought for sure that after this, you and Professor McGonagall wouldn't... you know... let me do anything the least bit dangerous ever again."

'Harry said nothing, feeling guilty about the false relationship credit he was getting. It was in fact the case that Hermione was modeling him with tremendous accuracy, and that if not for Hermione having a horcrux, the surface of the planet Venus would have dropped to fractional-Kelvin temperatures before Harry tried this.'

I agree with you that unicorn blood is more likely to be significant than the Horcrux in this scenario, and until this last chapter was posted I expected HARRY to think the same way, which is why his thinking stuck out to me as memorably optimistic.