This is my 5th year of mentoring, but when me and my fellow mentor started with the new team we were on, we recognized that a consistent image and a painted robot really does make a huge difference in your perceived competency.
There's something about taking the time to make your robot look good that also says you took the time to make sure your robot performed good. Granted the design you chose may not have been optimum, but at least you do what you set out to do.
We went with a consistent color scheme and a consistent mascot or feature that you will see on 2992's robots, we hope, for years to come.
2009 Robot "Dante"
2010 Robot "Chester"
It was as simple as a coat of paint and a plastic panel that makes all the difference in the world. Oh and of course we always put our hat on the robot somewhere. :-)