The Noctilux does interest me, but I've got the 50 Summilux ASPH and 50 Summicron already and the Noctilux price could get me a minty 21 Summilux and 35 Summilux FLE. It does produce some lovely images, but I know if I had it I'd use it and sell it within 6 months as the money tied up in it wouldn't make it worthwhile for me.
Indeed, that happens a lot more frequently than you might think. That and "buyer's remorse." On the bright side at least, you most certainly will not lose money on the deal.
Long term I don't know if I'm going to keep it either - but it's way too early to tell. I've yet to have a chance to properly shoot with it.
Either financially or just in carrying the thing, it does require a certain amount of... Commitment. And if you're not using it at f/0.95 most (if not all) of the time - then perhaps another lens would be a better solution.
The Summilux? Yeah, that's going to the grave with me.