Hi Charles, this is a question that seems to come up every few months or so here - it seems that there are those who love this lens, for example, for its small size and "fingerprint", and those who hate it due to a bit of softness wide-open and bad flare under some conditions. (Of course, there are also a few who are indifferent, and a few who swear by the ASPH version...)
So it's all going to depend on your personal taste - what kind of look you're after - your desire for a small lens (the pre-ASPH on a M camera will fit in a large coat pocket, the ASPH would struggle to do so), and whether you can tolerate some flare.
I personally own the pre-ASPH 35mm summilux, and it's not because I can't afford the ASPH version. I chose the pre-ASPH because in black and white (pretty much all I shoot) the lens has a special look, and even when i get a bit of flare, say from street lamps at night, it only adds to that look. ALSO, small size is very very important to me. As for sharpness wide open, I use the lens mostly with fast, grainy, black and white film under conditions with shutter speeds around 1/30th of a second - I'm quite sure that these factors are limiting the sharpness wide open more than the lens itself.
If I were interested in color work, and size didn't matter to me, or if I wanted maximum wide-open sharpness (perhaps under brighter conditions, or with a tripod), and if i wanted a "clean and clinical" rendition of a scene then I would chose the ASPH version of the lens.
By the way, i think 750 euros is quite a fair price if the lens is in good condition and with the shade. Always use the shade.
Good luck with your choice.