I'm a little lower on the ladder of "people-in-the-know" and speak only as a connected collector. Avoid damaged pieces if you are looking for future value.

If you find a rare piece that you need for your collection and it has a minor defect/chip that's not that noticeable, and you can get it for a really nice price, buy it. If you find a really rare piece that's worth the big bucks but it's damaged, consider buying it if you are willing to pay the price for restoration to that piece.

Artists Proofs, although rare, are not selling for what they use to. At one time, AP's would sell for 2-3 times the retail price. If you use eBay for price guidance, you'll find even AP's bringing not much more than retail. A damaged AP would sell for much less than retail, especially if the damage was obvious to anyone viewing the piece.

Bob