I don't envy Dmitri's position. Vladimir's ghost is not one with which to be trifled. But as a bookseller by trade and a Nabokov lover by necessity, I think we should save the manuscript.
Consider the case of Franz Kafka, who also wanted his work destroyed. It was his intellectual confidante, Max Brod, who decided to go against Kafka's wishes and publish his work.
Furthermore, if someone has the option to contribute art to the world (let alone something original, brilliant, or simply beautiful), what reasons does he have to restrain from doing so? In a time like ours, it is ridiculous to reject any intelligent cultural product. I feel Nabokov would understand this. Ultimately, it's a matter of weighing an individual against a society; no one (who really matters, anyway) would think any less of Nabokov (V. or D.) for allowing an unfinished manuscript be released into the public realm. Sure, the manuscript and Nabokov will, without a doubt, both be subjected to the scrutiny of unremarkable Ph. D. candidates and failed writers. But think of everything we have learned (and could still learn) from that man, that literary master.
One should not forget: The manner dies with the matter.
So, here's my last plea: Please, Dmitri, share with us your treasure chest.