Why have you connected the Colorduino to another Arduino? The colorduino has its own ATmega micro controller. You just have to upload the sketch to the colorduino not to the other Arduino... You can connect several colorduinos together over I2C. But you don't need another Arduino for that.
I've built a small robotic vehicle that uses 4 small stepper motors. To control the 4 stepper drivers (ULN2003) I used 2 74HC595 shift registers. http://www.bajdi.com/arduino-28byj-48-stepperbot/ So yes you can use shift registers to do other things then blinking leds
The UTFT and Utouch libraries take up quite a bit of memory. I assume you have edited the memorysaver.h file as explained in the documentation of the UTFT library? I was using a 5" inch touchscreen TFT (800x480px) with an Arduino Mega and switched to a Due for the extra speed/memory.
Strange that nobody has mentioned designer clothes? Gucci, Versace, Armani... Italy for me is "design", when the Italians make something it has to look, feel good in the first place. I like that. That's why I've owned 5 Alfa Romeo's, currently drive a Giuletta.
No the voltage will not be "stepped up". The ESC will probably work at a lower voltage but will not be able to give the rated current. So it's best to use a 4S battery if you want to use it at it's rated current.
Dagu is now selling a new kit that fits on top of the Rover 5 chassis: the service droid. I got an early version and just started playing with it. At the moment it's remote controlled by another Arduino through nRF24L01 modules. But I will add a raspberry pi and camera and try to do some autonomous stuff.
The technical details of the TFT show that digital pins 2, 3, 5, 6, 7 and analog pins 0-5 can still be used. I think the only way of connecting something to those pins is soldering wires to the pins on the bottom of the Arduino.