A buddy and I went to last years National and one dealer had a TON of these at his table. I don't know the year spread, but I think they are all from the 70's. He was at the Guersney's auction and won a few of the lots. He had everything from HOF'ers to commons, artwork, proofs and plates. We ended up talking to the guy for a while, he was one of the friendlier dealers at the show. I bought the Ted Williams artwork for $350 if I remember correct and my buddy grabbed the DiMaggio for $325. They both came from the 77 Topps set.
I agree these are undervalued, I was happy to get Ted at the price I did. It's a one of a kind piece, I'll never see another.