I really can't say whether or not the all german is actually any better as I have one of the .40 caliber that does not have the German proof marks. I can tell you that the fit and finish of it are as good as any I've seen with the proof marks, and I've yet to have a problem with it in over 2500 rounds. I asked this question here and on a few other boards after I bought mine and all I got for answers were "Make sure you get one with German proof marks..." Not one answer actually had any facts or data showing the non 100% to be of any less quality. Will it hurt the resale of the gun? Maybe, depending on who your selling it too. If they are one of those that needs the proof marks to feel good guys then yes, but if it's someone that just wants a good reliable gun then probably not.
Not that you'll have to worry about selling it anyway, as it will quickly become your favorite!!
I know I'll never sell mine, proof marks or not. The fact remains, if you have a problem with it, contact Walther, and it will be serviced or replaced by S&W like all Walthers here in the states are whether or not it has proof marks.
Hope this helps your decision.
Jay