#8, White Wall Tires. While they are important in Cars they are simply a proper detail in UP! Likely not connected. That would be like saying the blue sky in one movie is a reference to the blue sky in another movie.
References to films outside of the Pixar universe are endless, you could fill up the whole internet with them.
When Wall-E builds a statue of Eve from junk, her right arm is made from a Luxo, Jr. desk lamp.