The "most foolish" loudspeaker tweak/upgrade ... is

Thanks cdwallace; beautifully put. 

Thanks for the price updates geoffkait. Very encouraging.
I think age must be affecting my eyesight; as well as  ability
to follow threads and stay on topic; much less less learn anything
new. Cheers.
Soundsrealaudio, you're right about the money; however you can 
probably easier twist the arm of an audiophile just after he gets his
share of the proceeds from the sale of the home than when he paying the 
legal fees to get rid of the sac of hammers that's been 'hampering'
his enjoyment of music, as well as many other pleasure of life. Cheers.

Well...um...getting back to the subject matter of the thread: this one isn’t the most foolish because it’s free but imo it still qualifies as foolhardy.

You know the one where you place several coins of the top front edge of the speaker cabinets? Even Sam Tellig fell for this one; perhaps that in itself tells you all you need to know about high-end audio reviewers?

Now I’m all in when it comes to the practice of placing certain objects/masses on speaker enclosures in order to reduce cabinet resonances. But coins? Coins weighing several grams at the most are going to affect/reduce resonances on speakers weighing 1000X more than the coins?

Nyet. It’s expectation/confirmation bias in its’ most benign form and to me it’s sheer folly. But like I said before...it’s free so knock yerself out.

Gee, thanks for the warning. But if it's coins it not really free, is it?