Much in the same way that a shiny penny is "worth" more than a corroded one, would you prefer freshly-generated bitcoins?

There is no coins. There are records, which declare how much "coins" is assigned to which address. So there is no new or old coins but there is new or old blocks containing transactions of these "coins". Probably, coins assigned to block generated a while ago is more trustworthy then the one generated 10 mins ago just because you have more confirmations for older transaction. But currently you can't select which coins to send, so it do not matter anyway =)