I tried a few things that didn't work at all over the weekend. And it wasn't until this morning that I got the new site mostly back to where it was on Friday! At least I now understand what went wrong.
Adding a data type to your MVC Maser Page tends to break all of your menu links!
On Monday, I decided that the most complicated page Join.aspx would be better off on it's own controller, and I think that the Testimonials page will need it's own controller as well, but that won't happen until tomorrow.
For now, I'm posting to the MVC forum on the subject of How to get data on a MVC Master Page.
One suggestion looked promissing, but now I need to find a way to get a valid Request or Response object insde a Controller constructor, and until this can be resolved it's going to be a while before I can get the site working again.