I grew up in a small town and DQ was the only fast food place there so we went to it fairly often. But I can't say that I like to eat there very much.
Actually, I have doubts about any restaurant chain being a good longterm investment. Generally, there are so many eating places across the country that the competition must be terrible. I am sure there are individual restaurants which do great because of being the only one in an isolated place, etc., but for national chains it seems very competitive.
Of course, I don't know how much I know since the places that I frequent soon go out of business and the shows that I watch on tv get taken off the air.