Suggestion: the entire plot with super-Hermione is Voldemort’s practise at being nice. But he’s not being nice to Hermione, he’s being nice to Harry. He reasoned that this is a better way of stopping Harry destroying the stars than simply killing him (this way carries a slight risk but stops him having to kill his friend). He simply didn’t see it because is was a ‘nice’ method.
This would explain the extravagance of the immortality mechanisms he’s giving Hermione.
Hmm… some thoughts occur to me:
Firstly, he hasn’t used any of the muggle equipment Fred and George got him yet has he? But Quirrell’s got his pouch.
Secondly, this may not come as a surprise but he is likely to succeed since “HE IS HERE. THE ONE WHO WILL DESTROY THE VERY STARS IN HEAVEN” this could refer to Quirell, true, but I far expect it to refer to HJPEV due to the timing. Also note that Quirell says something about prophecies in ch. 108, but I can’t find the quote.
Third: obligatory wacky theory that his father’s rock is the Stone of Permanency. Stones == rocks, and he was given it by Dumbledore after all. And Harry’s magic interferes with Quirrell’s so it might shield the magic trace.
Fourthly: this is my first post on LessWrong, nice to meetcha!