He puts it right on the line when he answers a collector who wrote to him claiming that first day cover collecting is a racket perpetrated on the unsuspecting collecting world by unscrupulous dealers. He came to this conclusion when he tried to sell his home made first day covers to dealers and got no offers.
Herst replied, in part: "The cacheted envelope is not a racket. It is merely an added dimension given to a first day cover of adding brightness and interest to what otherwise might be a dull envelope."
A secondary point in Herst's answer is that the cachet is an extra thing -- a bonus -- above and beyond the stamp on a plain envelope. It is in a sense, and in the terminology of stamp collecting, a collateral item, like an autograph or related letter with historic interest; something that adds to and elucidates the stamp's subject. First day cover collectors are ahead of the game by having their collateral material built in with a special illustration (cachet) or pictorial cancel on their covers, both of which add interest and value.
Herst was still alive at the beginning of the first day cover art and hand painted cachet days. They have put a bit of a new spin on collecting styles as well as the resale value of some first day covers. Of course for collectors of the popular cachet makers the stamp becomes almost a secondary concern -- the first day cover becomes about the art.
Herst was something of a mentor to me -- primarily through his writings, although as collectors know he was very free with his time for anyone who seriously wanted to know more about the hobby, as I did. I asked him a number of questions and his answers never failed to be the most cogent and intelligent around concerning stamp collecting. I never asked him about the high valuations of art first day covers or what he felt their true philatelic value was. I do know one of his favorite answers to "What is it worth?" And that was "Whatever an informed and knowledgeable collector is willing to pay for it."