Is it true that a post-marked stamp has little to no value to the collecting community?
75% of the time, this is correct. But it is not
universally true. In some cases, a used stamp is more valuable that a fresh, never used example. Or, canceled examples are the only ones known (usually the case for early 19th century US stamps). And sometimes, it's actually the cancel itself that is the valuable thing. This may be the result of a post office only being open for a few days, or when a stamp gets withdrawn very quickly after its introduction, but someone was able to mail a letter with it. Or, if the cancel shows it was carried on a zeppelin, or by catapult or balloon mail.
There are collectors who go after nothing but cancels of a certain type or from a certain place. Others who collect mail ("covers") of a specific route, time, or event. Occasionally, the only known example of a stamp is found used, on a cover.
These appear to be Sc 657, 1058, and 1044, all from 1954, and aren't worth enough new or used to buy a pack of gum, sorry to say. Someone else will have to opine on the cancels themselves, though. Maybe something there, maybe not.