David, another one of those areas where you can get involved in whirlwind of opinions. The chrome exhaust tips were exclusive to the 71-72 Mach1 (body code 05) with 4 bl engines ONLY. Not even the premium performance cars, Boss 351 and C and J 429's received the chrome tips unless the 429's were Mach 1's.
And since you are an original owner of a 73 Q code Mach 1 you know as well as anyone that no 73's received the chrome tips on any body style.
As you also stated the dual exhaust rear valence and chrome tips were a very popular add on. With a retail price of $53.55 for the valance and $36.00 for each tip it was a affordable back yard project and gave you that "Look" we were all after.
The last set of NOS tips I saw (D1ZZ-5255-A and B) were in the $895.00 range!
And as we always say, it's your car to "Decorate" as you wish, we don't judge. This info relates to how these vehicles were designed by the engineers and how they were intended to leave the "Mother Ship".