As Kibblesmom mentioned, the tours changed last June. It is nice that on day tours, you can wander around the grounds on your own and enjoy the gardens and pools at your own pace. Before, it was very controlled and you were done and heading down back to the VC after 75 minutes.
You've figured out correctly what you'd see on the day tours vs. evening with the Upstairs and Cottages/Kitchen. "is it worth it?" to do the Upstairs vs. the Cottages/Kitchen, where you'd see the wine cellar and "B" house (not shown on the evening tour - A House is included on the evening tour). That's a decision you need to make based on your personal interests. The day tours are fast-moving - especially the upstairs - so even tho' you'd be repeating a lot of the rooms on the night tour, there is a lot to see that you might have missed the first time around on the day tour.
FYI, you are not allowed to stay on the hilltop between day and evening tours, so allow youself a gap in time. You might even want to consider a morning day tour, wander around, return to your hotel or go to the beach, and coming back for the evening tour.
It's a 5 minute drive to San Simeon - another 5 minutes to Cambria. Entirely flat and straight all the way. If you stay in Cambria, there's always a chance of raccoons or deer along the highway at nite, but that's rare.
To get the full experience you're looking for, do a day tour and then come back to see the place at night. And with the docents dressed in 1930's clothes for the night tours, it gives the estate an entirely different feeling as well.
Good luck with figuring out what will work for you, and don't hesitate to ask if you have other questions!