I finally got it working tonight.
PIC --> Raspberry Pi --> Android App
PIC is reading 8 analogue ports and outputting the data every 0.1s via serial over USB. The Raspberry Pi is running an Apache server and in response to an HTTP request to a PHP script, it reads the serial data and re-formats it into a simple fast JSON array. The Android tablet is running a custom app from App Inventor to make the HTTP request, get the JSON response and display the data.
The next step is to get a nice bar graph interface working and set up the Manifold Air Pressure (MAP) sensor I have in the car so that the thing can be tested reading boost from the supercharger.
Oh yeah and I have to get the Raspberry Pi working as an Access Point (AP) again. I did this before okay, but with a different wi-fi dongle. This is critical to using it in the car to send point-to-point data to the tablet.