Thinking about a part-time master's while working. Worth it, or expensive procrastination?

Self-taught, about a year and a half into my first dev job. It's going fine. But there's a nagging feeling about not having a CS degree, and I keep eyeing part-time / online master's programs (the OMSCS type) as a way to fill the gaps I know I have — the theory, the systems stuff, the things I've never had a reason to learn on the job.

The counterargument I keep hearing: nobody past your first job cares about the degree, you'd learn more just building things, and two years of your evenings is a steep price for a line on a resume.

Anyone here done a part-time master's while working full-time? Did it move the needle for you, or would you spend those two years differently if you could go back?