Welcome to the site!
I used to have a 2003 Matrix, (aka previous generation Vibe). It was a great car. Over its life it averaged 36 mpg over 68,000 miles with very mild ecodriving techniques and very minimal modifications.
Here is my garage entry that lists (with links!) my mods, and you can see my fuel log as well:
Details: Daox's Matrix - 2003 Toyota Matrix Fuel Economy - EcoModder.com