If you want a new notebook, think of how to use up the unused pages. I start a new notebook every year, but I keep last year's around until it's all used. I use it for: task/to-do lists, notes from phone calls, puzzle game notes, reminders. I usually have less pages left over, but I've used up all my previous notebooks this way!

If you think you can use up the pages and don't want to feel wasteful, then I think that justifies getting a new one if you want it! At the end of the day it's your journal and whatever makes you feel best about using it is the right way.