Smilingcat- If you do a 50 miler before the Cindy, you will be fine. Veronica has wisely pointed out the hills- and they really aren't that difficult.
There are 4 rest stops along the ride and if you really get tired, you can get sagged to the finish. Once you get to Tassajara school (the last stop and, well worth it), the rest is mostly DOWN. The only not so fun part is that some of it is in Saturday traffic so you have to be vigilent.
It should be a great ride this year as the wildflowers are beginning to bloom and it is quite green out.
It's lots of fun- people dress up and you'll see lots of different bikes.
Also, someone will set up a pre-Cinderella dinner- for Friday night not far from the start of the ride. I highly recommend that you come if you can. It's lots of fun and you'll get to meet some of the NCal TE'ers.