The doctorate would allow you to teach especially since AT is changing to masters entry level but outside of the teaching chance I do not believe higher level degrees result in higher salary for athletic training. Companies have been paying so little for AT for awhile now, why would they change. Also why I dont agree with the change to master entry level to only increase debt with no increase in pay I feel. My example is I earned my masters and then my wife and I moved back to her home state and I got a PRN job. Yes it was PRN and not full time but they did not seem to care much I had my masters and started me off right where they start everyone off. I got to know my supervisor pretty well there to the point I felt comfortable asking salary questions and they said even if full time I would have started at the same spot. They told me years of experience mattered to them much more than education level. Anyways my PT experience is below.
I originally thought AT was where I was going with my career. Graduated with my AT degree before the switch to masters entry level and then went on to pursue a graduate assistantship which was nice because you gained experience while earning your masters. I learned quickly though my experience in undergrad was far different than what it was like as the actual staff athletic trainer with the traveling and late nights/early mornings. I got married during my graduate program and started to see those hours and being gone is not what I wanted the rest of my life. But I enjoyed healthcare and knew I enjoyed the athletic training room time and really sitting down with athletes and trying to figure out what was going on to get them back out playing. That started to lead me to looking at PT (funny random note about that is my senior year in high school I took one of those career assessment quizzes in a class and go figure, PT was my #1 choice but back then didn't know much about it and everyone convinced me engineering is where I needed to go so never really researched it. Long story short, follow the hints and your own feelings not others.) I decided after talking with my wife that PT is what I ultimately wanted which is what you said is your goal too. That meant a few more prereq classes to take and with where we moved, little option of working full time since those classes were only available in afternoon and evening slots. But we sacrificed in areas and moved in with family to save some costs to help with offsetting the lower income of only one of us working full time. Then came time to applying for PT schools.
The first year I admit I did have a little bit of the "I am an athletic trainer" attitude and I have experience that others right out of undergrad do not have. Not that I am full of myself but I felt that would hopefully give me a little edge when applying but I learned quickly that certainly did not. I applied to three schools, all that did not do interviews and got denied with no waitlist opportunity at all of them. I never really got a time to sit and talk with other applicants and learn what they have done to prepare for applying to PT school and had I did more research and used this site more, because many are very open on here about their skills and preparation, it would have showed me just being an athletic trainer was not enough for the demands of earning a spot in a PT school. Getting outright denied did sting but I had already made my mind up that I would apply again if I needed to so I started to make changes to certain areas in my application. I retook the two classes I had C's in for prereqs and earned A's this time. I found new experiences to shadow and work experience to gain hands on practice. I rethought my letters of recommendation and was better prepared with my information for the individuals writing them for me the 2nd time. I also retook the GRE even though I hated that test but did do better so it was worth it.
I applied to more schools this time to increase odds, and earned multiple acceptances this time around. I understand its a burden financially and a very tough decision especially with a family to support but if you have a very supportive spouse and it is your ultimate goal to make a PT program, I say you go for it. Once I made the decision to change to PT, you sacrifice to make it happen but now that I am in, every sacrifice has been worth it. If any of my story sounds similar to yours than hopefully I somehow helped. This turned out to be much longer than I anticipated but I saw you were a fellow AT and in the same situation in many ways so figured my story could give some possible insight.
Last thing is I do enjoy AT but I don't love it. Many of the individuals I covered for in the PRN job told me they liked it too but also many would tell me they are already working on whats next for them too. AT is good but many I feel get burned out but for those that don't, they make good ones, and I respect them but I couldn't stay with it. I wont give up my certification but I know PT is where I want to go due to hours, increased settings, and what I envisioned the future as with family. I dont want to be working some high school game when my hopefully future kids activities are going on. Almost all PT's I observed with were done by those hours but I know that can vary. Long story short, if you are feeling any doubt about AT, I say go and give PT another go even if its your 3rd time. I know I only did 2 cycles but I would have done it for 3rd because I see opportunity with PT that AT didnt provide. Teaching is the different aspect you have that I never considered but my wife teaches and I give her the upmost respect because I could not teach no matter the age of the students.