Kidushin 31a brings the story of Dama ben Nesina and his amazing Kibud Av V'Aim which cost him a huge fortune. He was rewarded for his amazing Kibud Av V'Aim by one of his cows giving birth to a red heifer (Para Aduma) which was then sold for the same amount he previously lost by doing Kibud Av V'Aim. Why was there a need specifically for him to be rewarded in such a manner? Why could he not find a diamond that had such a value? Why reward him with a Para Aduma?
Ma'ayaneh Shel Torah quotes the The Chiddushei HaRIM that when Dama ben Nesina lost a huge sum of money because he was honoring his father, it created a Heavenly Accusation against the Jewish people.
By giving him a red heifer, G-d showed that while a non-Jew was willing to lose a large amount of money for a Mitzvah that makes sense, the Jews were willing to spend the same amount of money for a Mitzvah that is a Divine Decree and is completely irrational.
According to rashi in Bamidbar 19:22, in his second explanation of para aduma from rabi Moshe hadarshan, the para aduma comes to fix the mess from the eigel, just like the maidservant who cleans the mess in the palace that her child made.
Accordingly, the para aduma is representative of a good relationship between parent and child. Mr. Nesina was treated favorably by his son and the reward to the son was sign that his father was actually deserving of such behavior. As opposed to lets say his mother from story later in the gemara.
To demonstrate that although we see good rational reasons for kibbud av, we still must treat it as a chok and show unconditional observance even when it may not seem logical. This may be why it is listed in 10 commandments with the mitzvos between man and hashem and not with mitzvos between mam and man.