Enochian - if subsequent transactions by any person protect my previous transactions, then my whole point was moot. I think that's what you're saying.
Well, I took your comment about "forge an alternate history for the coins" to question whether creating an alternative block chain to the one containing your transaction would become easier with the passage of time due to advances in processing power. This doesn't happen, as subsequent blocks have increased difficulty factored in, so you're always adding blocks based on the prevailing system wide hash rate.
Bear in mind that the only thing the published block chain does is prevent double spending. All other attack vectors against Bitcoin, like stealing coins, or spending other peoples coins, are secured by the cryptography using the private keys stored only in your wallet.
If something bad happens to Bitcoin, it will more likely be a bug or the government, and not some inherent weakness in the thinking underlying the protocol.
