I ask you: what is ISO worth if the image quality is bad because of the lens?
There are shades of gray between good and bad, you know? First: The Tamron 24-70vc at much less than half the price than the new Canon has at least the same iq as the old Canon lens. Second: For a wedding, I won't need life-size prints with a pixel-sharp lens @21mp, but I will need higher iso capability that the aps-c sensor simply cannot deliver.
I'm fully aware of that. And I also know that my verdicts are pretty pithy.
However when referring to cheap Tamron and Sigma lenses, I didn't mean lenses as the 24-70VC. This wasn't one of the low-end lenses that I meant to refer to (e.g. 70-300 by Tamron or 70-300 by Sigma).
I'm sure the 24-70VC will do just fine, for it's not exactly cheap glass.
Who needs life-size prints? Very, very few people do. However, the crying was tremendous when the 1D X with ONLY 18 Megapixels was announced.
Also, I wouldn't count wedding photos into the "mainly stills" topic - there's still pretty much of a movement there, and one shot lost is one shot lost forever. While by doing stills, you can take your time.
In the end I didn't want to say that ISO is unimportant. I just wanted to say that if I had to choose between better lenses or better body, I'd go with the lenses.