I've bought a couple of coins and kept the emails and shipping labels from the man himself. Provenance will become increasingly important. There's already some Chinese copies, albeit blanks, copying the brass 1BTC Casascius design.
An original, even if it is redeemed, is definitely of interest to collectors. There are only a few thousand and it has become an iconic emblem of Bitcoin.
$325 for a Casascius blank is, frankly, ridiculous. There were 725 of those minted. Yes, that's a rather small number. However, Casascius coins have almost no aesthetic value and would be very easy to counterfeit should they continue to increase in price.