I just made an upgrade from to 8 to 16GB. You'll theoretically see higher power usage, but I couldn't quantify any difference in my experience.
The biggest thing I think you should be aware of, that I ran into, is that your hibernation and pagefile (at least in windows, not sure about OSX) will grow to 16GB each. 32GB of disk space can be quite the shocker, especially if you are running on an SSD with limited space like I am. In order to resolve this I disabled hibernation and reduced the size of the page file (in Windows).