I have a cousin who runs a small database and web design business, and the single most expensive item in his entire office is his chair.
That's right, his chair. His logic? "Hey, I'm going to be spending a lot of time in this thing. I want it to be comfortable and ergonomic so I can be more productive."
What is your writing space like? Is it comfortable? Are you efficient and productive there? Have you created a place where you can work intently and without interruptions--where you're shielded from distractions that sap your time and attention?
Ask yourself these questions, and then experiment with different ways to improve your work environment. Make your writing space a sanctuary where you can be as productive as possible.