We do it all the time when we travel by bus. I get easily car sick but at night when you can't see and the air is cooler it can be very enjoyable and you can both sleep. While we have traveled at night by car before and slept in the parking lot of a rest stop I wouldn't recommend it because you are over tired and it could be dangerous. But to save on hotel cost the night bus trick is just the thing. It is true, you spend more time on a bus than you would in a car, but since it is at night, you can afford an extra few hours because nothing is opened anyways. What I mean is if you were to travel at night by car and it would only take 5 hours to get there, what would you do at 2 am anyways? You would still need to find a hotel. So if you travel by bus and it takes 8 hours, you can sleep on the bus, save yourself the hotel and then you can arrive in the early morning hours and you are well rested and have a full day to do whatever you like. We have even returned home that night so that we didn't have to spend a night at a hotel at all during our trip. This did make us tired though so I would recommend at least a one night stop over if possible.
I have travelled overnight during which I slept on the bus. But it wasn't done to save money. Now that you have suggested it, I believe it would be a good idea. This is an option I would not have a problem in taking up without being forced by any circumstances because it would be a good opportunity to save a significant amount of money.
