Hi Jon, Congratulations on your up coming wedding, and boy ! what a place to spend your honeymoon.

I agree with Michael regarding the flight between Vegas and S/F. Not only will you miss so much by flying it will also cost you not only the flights but also a one way drop off fee for a car rental. With 3 weeks you have plenty of time to explore the area and Death valley and Yosemite are two places you do not want to miss.
You might also want to consider visiting the wonderful parks in Utah, such as Zion and Bryce canyon, just a few hours from Vegas.

Here's a good list of ideas in the area to get you started.