The answer to both questions would be yes. After buying the QB Boost I was able to get Matt Ryan to a 97 overall and buy him superstar development (he starts with normal dev) in 2 seasons. It also seems to be good when you have a back up QB riding the bench that you want to develop. So I personally would say it's worth it.
When you buy any of the coach packages you keep them permanently. The only time you lose the boost packages is if you retire or switch characters (I think you keep them if you get fired).