Hi kmw5,
If you haven't already paid for your Global Entry application, and still have a US address, there are a few travel credit cards you can sign up for that will give you a nice travel points bonus and reimburse you for your Global Entry application fee. That's how I paid for my GE and my mom's.
The interview is quick and easy and the CBP officials are super nice.
As for demand, there was no one waiting when I went for my interview last year, but the appointments on either side of my mom's interview this summer were taken. We also had to schedule my mom's appointment further in advance than I had to schedule mine. I think it's becoming more popular. It's definitely been worth it for me. It also means I don't have to get a Real ID drivers's license.