I find it helps to intentionally "break it in". Draw something silly, write a bad poem, write a journal entry upside down, freehand a chart/page layout with bad lines, etc. Do something to make it no longer "perfect" to get yourself out of the mindset that the paper pretty notebook deserves a level of care and attention you find exhausting and ultimately disappointing when you can't keep an insane standard of care.
What makes them nice is the experience of writing on them. Not that the writing in them is a certain quality. Do you go back to your spiral bound notebooks? What if that content were in nice notebooks, would that change your behavior? I'll bet it depends on the content, not the paper it's written on.
If you stop writing in them as soon as your writing devolves, let it do that immediately and keep writing. If you want a perfect notebook, the only way to do that is to exhaustively transcribe from another source, and who has the time to do that?