What's with sudden "boom"?

I just watched two cards close for what look like Ebay records..
1960 Topps Willie McCovey rookie PSA 8 (not centered well): $713 (has sold for around $500 - $600 when well centered)
1967 Topps Orlando Cepeda PSA 8: $320 (well centered, has sold for less than $200 in the past for nice 8s)
I don't watch enough other vintage items to notice a trend, but this seems kinda sudden.
1960 Topps Willie McCovey rookie PSA 8 (not centered well): $713 (has sold for around $500 - $600 when well centered)
1967 Topps Orlando Cepeda PSA 8: $320 (well centered, has sold for less than $200 in the past for nice 8s)
I don't watch enough other vintage items to notice a trend, but this seems kinda sudden.
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Im not too familiar with the Cepeda but the McCovey I used to track often. A couple of years back I had 2 complete 1960 sets, both of which all the star cards were graded and I know I didnt pay anywhere close to that for the McCoveys in my set.
I have noticed similar trends with other high end HOF'er cards lately though. It seems the stars in high end condition are fetching premiums while everything else is taking a nose dive.
-- Yogi Berra
<< <i>That's BIG money for a McCovey 8. >>
Yeah. I figured it'd go for something closer to the low $400s with that centering. Guess not.
If a poorly centered 8 goes for that kind of cash, I could only imagine what a nicely centered one would go for.
I've been hunting 8s for a while, but if they're going to go for that kind of money, I think I'll start hunting for a high-end 7 instead.
WTB: 2001 Leaf Rookies & Stars Longevity: Ryan Jensen #/25