I don't do anything according to a predetermined plan. I go as far each day as my mood and body dictate. Sometimes I take a rest day because I really like a camping spot. I've taken a rest day on the Fourth of July several times to avoid dealing with a full campground. A couple of times I've gotten really sore and tired after three days of riding when I wasn't in the best of shape, and have taken a rest day to try and recharge and recuperate a bit. I have a knee that starts to hurt after a lot of climbing. When it gets bad a rest day helps. Once I get going I tend to take very few rest days, as long as I'm feeling fine. If there was a horrible rainstorm I might hide out in a motel for a day.
I also like short days occasionally - 25-30 miles. I usually start out easy, and sometimes later when I start to feel tired and downtrodden a short day is just the thing.
On rest days I generally do very little. Lots of reading. Walking around a little. I don't go sightseeing; I want to rest.