I'm watching price on these recent GG auctions for sure. It's so hard to gauge price on these...it's been all over the place for years. The letter should help the value of this set a bit though. I'd agree that $3K per each is a pretty good deal given what guides have historically listed these at in the past.
As an aside, I've just recently acquired another set of GG #1 & #2 via private sale that I believe to authentic. Based on recent auctions (including this one) I got a really good deal on them. I'm going to have Eastman, Laird, and/or Lavigne take a look at them sometime soon. This year at FCBD both E&L authenticated and signed the copies I've owned for 20 years. That was awesome. If they authenticate and sign this new set I got then, depending on what the market dictates, I may sell them (or might trade for Turtlemania Gold).