Over the years I've evolved my philosophy on upgrading to simply replacing things as they wear out with a part that offers an improvement either in durability or performance. But the part I'm upgrading to can't sacrifice durability for performance. The exception being contact points. If the seat and the tape or grips doesn't work for you, you've got to change them right away. Accessories are good though. Once you have the essentials you can pick up something new and fun occasionally and if it turns out it doesn't really end up that useful you're not out that much.