Our all electric home has registers in each room. Is it more economical to lower the temp setting in the rooms we use from 70 to 55 at night and turn them back up when we use them again or just leave the temp setting alone at 75 all the time?

Where are you? 55 is too cold for me at night, and 70 ain't enough during the day. 45 during the day and 30ish at night here. 77 thermostat setting, bill is $210-$250.

75 is pretty high if you are in a colder climate and the heater runs all the time. We have our thermostat set at 70 during the day and 63 at night. With a programmable thermostat, you can have the heat come up 1/2 hr. before you get up. 3,500 sq. ft. house, 2 zones, Atlanta area, $175 last bill,we also cook and heat the hot water with gas.

I just read a site claiming that a big range isn't a big savings, while a medium range is more worth it. I'd say a range of 5 degrees. Rooms aren't insulated in inner walls, so heat just leaks in or out anyway.
I don't sleep well and get up a lot, so this is the first year I'm keeping my heat at 67 all the time. It's working out fine, according to usage so far.
Summer sun is a huge energy saver. Open curtains, and be sure to take out screens in winter! Close doors to north side rooms and take advantage of south rooms on sunny days. It can be 20 out and my heat doesn't come on at all from 9 to 3.

I think there are two different questions here:

1. Is it best to keep heat turned low in unused rooms?
2. Is it best to turn down the heat in all rooms when away, and turn heat up when at home? In other words - does the extra energy required to reheat the rooms from, say, 60 to 70 more economical than keeping the house at 70 all the time?

The answer to 1 is yes - if you have multi-zone heat and can shut off rooms that aren't use that is certainly more economical that heating the entire house. However, it's best if you can shut off airflow into those rooms - for example by shutting doors - so that the heat from occupied rooms doesn't go to heating the unoccupied rooms. This is especially true if you have a multi-story home and the unoccupied rooms are upstairs (heat rises).

The answer to 2 is a definite yes. It's easy to show that the energy required to reheat the rooms when you get home is less than the energy that would have been required to keep those rooms up to temp while you were away.