First of all, learn to make the most of the balance you've managed to strike, which is known as the "state of flow". You reach this state when the activity you're devoting yourself to is in proportion to your abilities and through it, you free yourself from the frantic search for approval and recognition.
Everything would be perfect if it wasn't for the fact that you sometimes feel like you've achieved all you can in your current role.
Now that you find your job a walk in the park, you'd like to spice things up and set yourself a new target.
Your career brings you personal fulfillment because the objectives that you've managed to reach make you feel worthwhile.
It's highly likely that your professional satisfaction is reflected in your life outside the workplace as peace of mind and self-confidence encourage fulfilling relationships.
The lack of career progression can, in the long term, be harmful to the quality of your work: consciously or not, you might find yourself limiting how much you push yourself, so that you don't get there "too quickly".
Also, work projects are, to an extent, what keep you going and they give you the courage to overcome difficulties.. . their importance shouldn't be underestimated!