If you think you would like inspecting full time and have the means to do so I would recommend it. You can certainly make a living with "just that card". Of course it depends on the economy in your location and if you want to travel. Like welding the more processes you can do the more options you have. But the guy that only welds pipe is still very employable. Same with CWI. Many ND Examiners only do UT or RT or VT. Some do all.
Similar to you I was a welder/fitter for many years, supervisor, self employed for last nine years and last year I decided to try to get my CWI. Something I wanted to try for many years. I had friends with similar experience that took test one passed one did not. If you do go for it you should take the seminar before the test. I would not have passed if I had skipped the seminar and not studied before I went and at hotel at night. I payed out of pocket and would not have been able to live with myself if I had failed and not given it my best shot. It was not easy.
After passing test I have been offered CWI jobs from the NDE companies that do our RT & UT's on projects, and some out of state opportunities. Not blowing my horn just letting you know that a CWI cert is enough to get hired at first. I only test our welders inhouse(only seven welders presently) and responsible for our welding projects especially the RT & UT jobs so I am not a full time CWI by no means but I would like to get more experience.
For insurance purposes many jobs require more frequent inspections or dedicated inspectors and with the nuclear plants on the rebound, ethanol plants and other industries I see a need for CWI in the future.
You are correct in that many job listings want UT cert with CWI. Don't let that stop you. Good luck with your decision.