it is entirely personal choice. there is no gurantee a PHD will make more money than non phd .That all depends on leadership skills in USA.Techinical people will always remain techincal .Atmost become techincal manager if the person has so many years of experiences and has little interest in managing small groups.If you are aiming high PHD just to make money then forget it! But if you enjoy what you are doing .i mean studying then what can you ask for more.8-5 job is boring as hell!! Phd you do everything in your own pace .it is kind of fun at the same time challenging. So , money should not be a factor to go for phd.Phd is something a way of achieving nirvana hahahah kinda in knowledge in your field of interest. So,at the end it is personal choice how much you want to earn and learn.Do you know that there is not a lot of difference in earningin life time in usa with person with highschool degree compared to college degree.