I am not sure that those jobs are better in the sense of pay or hours. The basic resp therapist or rad tech started out about 2-3 dollars less an hour at my old hospital. They also have to work night shift and weekends.
I have never known a registered nurse to become a resp therapist or rad tech, I am sure it happens but I have a relative who went back to become a RN after being in radiology. There are also other careers such as physical therapy assistant that may be on par.
It is important to like what you do, you can work in radiology department as a RN. The strength of a RN degree is the flexibility, opportunities and demand. Once you get about 5 years of hospital experience, depending on where you live, there are a lot of options out there.