Whether or not it makes a difference really depends on whether the RF flare of your M6 causes you irritation or affects the way you work with the camera.
I live in a bright sunny climate and RF flare with the M4P, M6s and early production M7 I have used has been a problem and I have missed shots because of it. I can only speak for myself, others report having no problem with the M6 in this respect. It seems to be related to individual photographers working methods and subjects they shoot.
If flare is a problem to you then the upgrade will make a real difference and would IMO be worth the expense. However, it seems to be the fashion these days to get an upgraded VF even when its not absolutely required for a particular photographers on the ground needs. 135 pounds buys quite a lot of film.
Apparently,according to Leica,the turnaround is approxomately 7-10 days.If I wanted to go the whole hog and have the windows replaced with the MP's multicoated ones then the camera would have to go back to Germany on account that they're hot-bonded in,for which Leica would want the thick end of Â£450.I think I can live without those!
You're quite right Craig-that kind of money buys a lot of film but I do find that the flaring problem always seems to happen at the most inconvenient time but I'm also used to using a Rollei 35 and I have become particularly adept at guessing the distance !