Why was the Shofar that was blown on Rosh Hashanah in the Beit Hamikdash plated with gold?

Rabbi Yechezkel Landau, famed author of responsa נודע ביהודה answers this question parenthetically in a letter written to his student, author of responsa תשובה מאהבה. Here is what he says:  

ולעניות דעתי נראה דרבינו [הרמב"ם] סבירא ליה דכל הציפוי לא הי' אלא לנוי בעלמא משום חבוב מצוה ומעצמן הנהיגו כן ולא מצד הדין. 

[Translation: It appears to me that Maimonides is of the opinion that the Shofar was plated in an expression of endearment towards the Mitzvah, and this practice was initiated by the people themselves and is not a requirement of the law.] 

Clearly, then, this was the minhag in the Beit Hamikdash to bring honor to the mitzvah, whose Biblical source would only be the general instruction to be mehader bemitzvah, as it is learned from the pasuk, זה א-לי ואנוהו.