Over the past 12 months, I do see that $1,000 range you're talking about. As noted, eye appeal is a big factor. Others include the auction house, the grading company, the amount of Red remaining, amount of luster remaining, and time of year (seasonal factors).
While a $1,000 range sounds like a lot, when you consider it's $2750 to $3750 it makes more sense. Most of them came in right around $3000 to $3200 with buyer's premium (if applicable).