I came into running from a boxing/martial arts/bodybuilding background......and to be honest, much as I love my running, I don't want to end up having the typical upper body of a distance runner. Its just a cosmetic thing. For as long as my running times keep improving I'll keep it up.
I have given up bodybuilding but still incorporate high rep (10-20) weights exercises for every muscle group (I do an abdominal workout too). It might have some benefits to me as a runner.............but honestly, I'd imagine that the weight I'd lose if I gave up all weight training would possibly benefit my running more.