You said decoration "actually helps you stick with it." I gotta disagree on the cause. The decorations don't make you consistent, doing it every day does. The fancy stuff is just the reward you give yourself for already doing the work. If you rely on making it pretty, you'll skip it on busy days when you can't decorate. The habit has to be separate from the art.
But saying the fancy stuff is just a reward kinda misses it. If making it pretty is what gets you to open the notebook, then that's the whole point. Are we really overthinking colored pens this much?