I'd say it's 100% worth it. I'm also in my late 30's. 4 years ago I failed to pass the phone screen with F and G (and failed 7 out of 8 onsites with other companies) but this time around I passed the hiring committee at G. I ended up declining for a pre-IPO startup though.
I had the same issues as you last time around. I struggled with System Design because I had no clue what the end goal was. It's silly that you're being asked to "design" systems in 45 minutes that have taken teams months or years to build.
The bootcamp really helped me with my anxiety. I ended up doing about 10 mock interviews which really helped calm my nerves during real interviews because I knew what to expect. I think that's where social anxiety comes from - when you don't really know what to expect.
I also used a Space Repetition Software program to help me with memorization.
If you post your email, I can email you if you want to learn more about my experiences with it and answer any specific questions you have.