Just to update my post above, I'm now half way done with the program and have ZERO regrets about not taking on more debt to go to a fancier-sounding school. School has been less exciting/inspiring than I was hoping it would be, and if I had taken 50-70k in loans and was still feeling this way, I'd be pretty damn pissed off about it!
That's my story.
I finished my Fulbright and decided to come back home and try to make an impact in my state. About 8 years of policy work later (with some international experience in between) I'm towards the upper end of the $70 - $100k range...in the U.S. South...doing the work I've always wanted to do. I've been able to do some really high level stuff and really put myself out there in ways I would never be able to do so in a D.C. or New York, but I'm definitely not some savant or anything. Just really went after what I wanted. The most important of advice to anyone though is work. You'd be surprised how you can have any job be exactly what you need it to be in the long run.
The stuff isn't rocket science, yet some of the most brilliant people I know struggle with all of this. Folks who are much smarter than myself, yet I've been able to get through all levels of education without having to take out a single loan. Ever. I'll be able to go to HKS without having to take out a cent in loans. In fact, I didn't even have to pay the dang deposit nor application fee. It's not to big myself up at all. I don't have some secret formula. I just have good experiences and the right background, which I crafted over time and very strategically. I guess I put all that stuff together in a cohesive enough manner with my application. You can too, though! Probably better than I can. Just trust the process.
So to more directly answer the original question. No, taking out all that money to pursue this particular type of education is not worth it and never will be. I believe you can always find the right school who will give you the right money. I encourage you to reevaluate your approach to this process, whether it be the testing (I didn't study much for the GRE and was going to really concentrate on retaking if I didn't get in), essays (I told stories that wrapped around both my work and what I envision being able to do), and coaching up my recommenders (make sure you don't duplicate your resume and help them dig deep).
I encourage you all to simply not rush any of this. It will work out to your benefit if you don't.
I'm at SAIS, and I can tell you that you'd be very competitive here. It is quant heavy, so they get really excited when someone who can handle really high level math/econ arrives.
As for age and career change, myself and several of my classmates are older come from areas far afield from international relations and public policy. I have found this to be not only tolerated, but celebrated as the professors will lean on students strong in certain areas other than the traditional poli sci/econ track, and try to bring the knowledge of the unorthodox discipline into the courses. And don't worry about the first GPA over ten years ago. You've demonstrated more recently that you can do well.
Good luck. I'm sure you'll have several great options.