Looks like drby got it on this one. Just FYI. I pinged the VS team to ask about this and here is the response:
"There is no way to reverse the command automatically. For it to work as a toggle we would need to save which toolwindows were auto hidden and which ones were not when the command was run, which we don’t do (it would cause lots of interesting persistence questions, across profiles and VS sessions)."
The idea of a "Unhide All" command is what I suggested. So if you hide all then you can unhide all as well. There might be some windows you don't want to unhide but the 1 or 2 extra windows is better than not having an unhide IMHO.