proofs vs. the regular edition and of course there are artists
who charge more than double for artist's proofs. You must
be the judge!
The value of an artists work really derives from the
artist. There's a popular story of Picasso sitting in a Paris
café having an afternoon refreshment, when a lady fan and
collector of his work comes up to him.  After sincere
proclamation for his paintings she nicely asks, if he would
autograph her napkin. Picasso signed the napkin but was
not turning it over. As the story goes he wasn't doing much
of anything until the lady says, "well may I have it?" To
which he coolly replied, "that will be one million dollars,
p l e a s e . "  Of course the lady was dumb struck and she
looked at him as if he were crazy. After a moment to gather
herself she said "but it's only a napkin." Picasso then went
on to give her the shortest and most complete education on
art in history when he said to her, "It's never the
artwork, it is the signature."
Of course not all painters grow into a Picasso and
sadly there are artists who have so boosted the value of
their artist's proofs, they can't sell anything else. When an
edition is released all the artist's proofs are sold out almost
overnight and then the rest of the edition sits there slowly
decaying over time. Many collectors are ill advised and
well trained by their gallery or art dealer's marketing
machine to purchase only adjunct proofs and to never touch
the rest of the edition.
This over-marketing of adjunct editions becomes even
sadder when many artists who are quite good fall into its
trap forcing collectors who enjoy their work to avoid buying
regular editions, because these are collectors who actually
want their artwork to appreciate in value and not to just
enjoy the work.