Thanks, guys.
So it seems I have learned:
a) my reading of the USED catalog value is wrong

, because I was looking at the RH column (which is for blocks of 4 / coil pairs, as per p.xix of the PSS Bureau Catalog, 5th ed.) instead of the L (singles).
b) the P.10 New Haven stamp in my original scan is indeed "worth" only 15c ($6.50 in a block of 4, though - wow!).
c) the Bridgeport stamps are somewhat better than (my) average -- the P.10 version on the L of my original scan is cv $1 and, unusually, the more recent P.11x10.5 in center of the scan is rarer, at cv $2.50 (blocks would be $7.50 and $10).
d) wt1 and I both need to check our abandoned blocks and pairs ASAP!
Thanks!