My definition of personal development (which I tend to use interchangeably with personal growth) is taking conscious responsibility for the changes we inevitably undergo by being alive.
Do you want to grow or do you want to contract? Do you want to grow in a deliberate way or a haphazard one? The worth of personal development to you as an individual depends on your answers to those questions.
You can change in the negative (not in the sense of good and bad but rather positive space/negative space) by contracting or by becoming ever more entrenched in the things you have been and done and nothing more. If you see your potential as ever-expanding based on age, staying the same leaves you smaller in comparison to your potential, thus the ratio of actualized potential to possible potential is going smaller. AKA negative growth.
Or you can grow just however you grow. Most people (barring developmental arrests or trauma or very limiting cultural pressures) continue to expand; they just don’t think about it or try to expand in any particular way.
Or, you can choose to direct your growth and attempt to optimize it (in whatever direction makes sense to you, whether that is specializing and become absolutely masterful in one direction or pushing to expand in several strategic dimensions).
The last is what I would call personal growth or personal development. And you can do it in so many ways. Personality and psychology frameworks are one. Art and aesthetics and philosophy are another. Skills. Experiences. Relationships of various types. There is an infinity of ways to intentionally change and grow.
Whether directing your own growth has value to you isn’t up to me. Only you can decide if the reward is worth the effort.