Well, I don't think it's been ruined by Twilight but then I never got into Twilight. Never read the books or saw any of the movies. I think you're right...the association will fade. I wouldn't worry about it at all.
I think it's an okay name, but I prefer it in the middle name spot. As a fn, it definitely needs a nickname. I've never heard of
Ned as a nn for
Edward. I don't love Ned...it kind of has the same too old-fashioned feel that
Edward has. I like the classic
Eddie nn better.