Mr Wales wanted it, so I am going to give him mine...
For me, I see two main areas where the money could be spent:
1- Text books copyright buyouts. Primarily historical reference material.
2- Commisioning original photographic and illustrative content for Wikipedia
(under the SA or GFDL, of course).
Let's face, $100 million can buy a lot of stuff. Certain established text
books being licensed under a SA license would do a world of good.