At the end of the day, if you like the lens for it's abilities and features and can afford one, then go buy one. It's as simple as that. For me, my mkI copy has been the backbone of my photography for the last 7 years. It's not as sharp as my primes but it's certainly a strong performer and it does so much so well. The newer mkII has a lot of additional benefits over the mkI but a few areas are weaker. The Max Magnification figure has dropped dramatically, which indicated focal lenght breathing at 70mm at MFD. For most user's this isn't a problem. But for wedding photographers like me who don't want to take a massive bag to each wedding, ring shots now need a dedicated macro lens. Will the rumoured IS version correct this? Who knows. I'm one of the few photographers who seems to like the reverse zoom and large hood of the mkI and was dissapointed to see this has been normalised...a pity, the old one was fantastically quirky and very functional. Last year I was on the Northumbria beech photographing a Bamburgh Castle with the sea / coast creating a nice leading line. The sea was craching in quite violently....my colleges who were also on the shoot were using a 16-35IIL and were constantly wiping sea spray from their objective lenses....my 24-70I's and it's deep hood had no such issues.
Becuase this lens was different in it's function, it attracted a lot of unwarrented critism from people who hardly used one, there is a ton of web "opinions" which are based on re-gurgitation from the various web reviews and a quick fondle in a shop, but these opinions are not based on real world application, where these quirks are seen to be a really well thought out rationale with great benefit. This pressure (meme) has caused some obvious design changes which appeases the internet masses as a positive....but not the photographers who valued such a useful but quirky design.