I meant why would older Bitcoins be more valuable as a currency?
If the chain splits, then older coins will be spendable on two different chains, and they will therefore be more valuable. It's not "older is better", though -- coins would be divided only into categories of "before the split" and "after the split".
I believe that is only one of the issues with forking the chain.
Consider this, if you were to fork the chain at some time point, you would also need to change the transaction format going forward, or else, your spend in one chain could be replicated to the other too.
Think of the confusion it would cause if you could post an address and have it a usable address in both chains? Best you could do, I think, would be to allow addresses from the previous chain only as inputs to transactions, and use a whole new address format going forward... to prevent each system from validating eachother's coins.
Not to say that it can't happen, or it wont ever be tried (hell I know a guy who had $500 and needed $1k tomorrow so he figured his best bet was to buy scratch tickets), but I can't see it turning out well, or being useful for very much.
Maybe as a game currency or something where you just want to give people an incentive to play. Of course, to "play" they would need the private key info from their real bitcoin wallets to sign transactions... which would be pretty safe if you used a new format that differed from real transactions but.... your game idea had better be damned good if you think many people are just going to let it grab the private keys from their wallets for in game use.
Really, if someone wants to change the rules, its best to start a whole new parallel block chain (or implement some of what was talked about with bitdns of using related block chain that can be simultaneously mined)
I go back and forth on whether I like the fixed total money supply of bitcoin but, thats what bitcoin is, change that and you really do have a different beast.