I agree with Fogmaker. I have good copy of the 24-70 Mk1 that I've used for 4 years that has never let me down. I tested out a Mk2 and decided definitively that I would not be upgrading to the Mk2.
The main advantage of the Mk2 that I could see is that it is a bit sharper at f/2.8 and that it's better at the very corners. In my own tests, I couldn't see significant differences between the lenses at f/3.2 and smaller except at the very corners.
For your type of shooting, edge-to-edge sharpness doesn't matter too often because the extreme corners of your frames are almost always part of the background bokeh. (If you were a landscape guy, the Mk2 would be a lot more compelling).
The other glaring difference to me is the way that the starburst/sunburst pattern is different in the Mk2. I know a lot of people love the newer lens' super starburst pattern but I prefer the more understated look of the Mk1.
I doubt that there would be any discernable difference in print if you shot them with a Mark 2 vs with your Mark 1. Two questions to ask yourself: 1) Do you think you're losing clients because you're not using a Mark 2? and 2) Do you think your clients would pay 20% more for your shots if you had a Mk2 instead?
Your pictures are terrific. I would be willing to bet that the answer is 'no' to both questions.