A basic question. When you back up a wallet you are only backing up addresses that have been used already, is that correct? In other words the wallet does not start out with any addresses and each time coins are received, if you generate a receiving address, you need to create a new backup?
I think the wallet starts with one address, obviously it has a zero balance, but the private key for that address will be backed up when you backup your wallet. You have to generate a new address each time you need a new receiving address, and in that case you should create a new backup. This applies to any cryptocurrency, because you need the private key for an address in order to spend from that address. You can re-use the same address over and over again, especially in the mini-blockchain scheme, since each address has a corresponding balance in the account tree. We actually discourage sending coins to an address which doesn't already exist in the account tree (aka an empty address) because it increases the size of the account tree.