I'm really thinking about getting the 24-70 II. I'm mainly a hobby photographer, but I do like having the best.
The way I see it that buying any expensive lens, if the quality is up to par then the lens will last me 10 years. It won't really depreciate like an SLR body would.
Buying older lenses you always have that thought that you might need to replace it with a better model or you've just not got the quality and look for an alternative or a prime.
I'm basically trying to make myself feel better buying the 24-70 II. Is that a justified reason: