One tricky thing I noticed which comes into play when you have a whole dashboard full of little key measure widgets (ie a gauge chart report which renders as a single colored number). Typically you put the widget and you use a text box before the widget to explain what the key measure is.
I see you have to be very careful on New Dashboards because now that these widgets dynamically jump all over the place as you move them around it's very easy to accidentally separate the widget from the text box that explains what key measure of the Widget refers to. You could easily end up with a whole column of Key Measures which are misaligned with their labels. Also, the new widgets are arguably prettier, but are longer in height, so the lower ones are not visible without scrolling.
There is certainly an argument to be made for giving Admins the ability to select which style of Dashboard they want to use.