I used the Di2 shifting on the Madone I rented for my trip to Provence. Frankly, I don't see what the big deal is. So, you tap the shifter a little lighter? I never have had any trouble with my mechanical Ultegra on my current or 2 bikes before this. I didn't find the Di2 shifters smaller, either. Of course, I have an in home mechanic who keeps my bike perfectly tuned, so maybe that helps. I am very petite, but I don't have teeny hands or fingers, though. For me, it's all about the reach.
The experience with the rented bike made me happy I made the decision I made when I bought my Silque. DH got Di2 on his new Time he bought after his crash last summer. He loves it, but he loves anything new, technology, etc. I think it's kind of a waste of money, but if it's going to make a difference for you in an ergonomic way, than do it.