I have never really liked the idea of First Day Covers.
I appreciate the fact that older stamps have additional interest …and indeed value when they have been posted on the day of issue. But …for me, it works best when it is “accidental”. When it is contrived and with a fancy envelope and the stamps exceed the actual cost of posting, then I really think it is for purely Philatelic purposes and not as interesting. Indeed many “modern” FDCs lose value by having an address on the envelope.
It is of course true that the cancellation…which is often artistic …is usually very clear and the stamps are ” very fine used” and many collectors like this. For me, I collect mint and used and I expect “used” stamps to look as if they have gone thru the mail.
I do of course have some FDCs but these mostly date from the 1970s and my “learning curve”. I also have some later FDCs which I bought primarily as souvenirs.