I have taken Word, PowerPoint, Outlook, Access and Excel... I don't think I am forgetting any!
I was an instructor at a private college before I became a VA and taught the Business Administration program. So, I was able to take my tests for free.
While they were definitely good to take and I got these great certificates from Microsoft, I wouldn't say that they helped secure any amazing positions (nor did my clients care that I had them!)
That's just my two cents.