Good job! I find that an Attiny running I2C is a very convenient way to hook up other parts of a 'bot. Personally, I use it for battery monitoring and power control (turn motors, fans, servos, etc on/off)
Also, technically, averaging multiple samples *is* a kind of oversampling with filtering! Now you're offloading it to the sensor-specific controller, and using slightly fancier math than a plain rectangular window, which probably makes life a lot easier on the main controller.