Try the 50lux first before you decide on the Voigtlander 50 F1.1. Really a different league in sharpness. Can't explain more until you try it.
Leica Summilux comes with different version. The latest version is the best ever made with the sharpness and smooth bokeh. Older Summilux can be bought at a much lower price than the latest model, which I bought at $5,300 a year ago for a nice Chrome set.
For older Summilux, they are not made with the Aspherical elements, which Leica priced most of them double compared to their non-asph ones.
Walk around Peninsula shops for the old Leica lens to know roughly market price (mark down their prices of course, as the shops are over pricing some old lenses as well).
Happy to discuss more on Leica lenses if you need more info since I have been a Leica M9P user for quite a while. Don't want to get out of topic. You can PM me.