On the topic of Summicron vs Summilux... I've been debating this myself as well. It's not just that I don't need the speed (It comes in handy, for the types of weddings that I shoot)... But it's more that I'm actually starting to like the look I get from the Summicron lenses over the Summilux lenses. Even stopping the Summilux lenses down, I don't get that look.
I'm thinking of dropping my (almost every current Leica lens), for a select few tight work lenses.
I think I could get away with 35cron (or FLE if I chicken out and decide I need the extra stop), 50APO (wouldn't keep the lux or noct), 90APO (or 90elmarit which I just ordered because I wanted to play with something smaller then the 90APO). Then I can get rid of my slow and fast wides, and totally drop the idea of keeping my 28s and 75s lengths.
Who knows, but it's been on my mind for the past few months.