You can change your keypool to 1000 if you want keypool=1000 -keypool=1000 I have encountered strange things when you run out of key addresses and you are still mining blocks (primecoin) but only if you have two or more of the same wallet.dat running on two different nodes and you start sending coins from the wallet you don't use to mine with it starts to place the change in keys another wallet does not control and creates huge issues and coins usually disappear and don't show correctly
but what happens in a wallet.dat is not really important if you know what you are doing because the coins are actually on the blockchain and not in the wallet.dat they are as you know just the keys to the blockchain and should be treated as such! but when you run out of keys on one wallet.dat and the other still has some and you send coins around the change gets put back into an address the other wallet.dat might not own
My advice is not have the same wallet staking on more then one node to avoid these issues and yes back them up every so often its not really that important or necessary though.
If you have one backup from when you first made the wallet then that is enough forever. To be able to control those coins i usually backup a wallet when i make new addresses but never use them unless i have an issue kinda like a system restore point or points you can check to see what programs are effected i note the same things fro each backup.
SVN rev 163 (ver 0.3.13.3) has the key pool feature. Pre-generated new keys are aged in a queue before use, so that backups of wallet.dat hold keys you'll use in the future.
For now I made the default pool size 100. It can be configured with -keypool=. Be aware, it takes a little time to increase the pool size, so don't go crazy with it. Disk space is about 1K per key.
I have not addressed the recovery side of this yet. If you actually did restore an old wallet.dat, I think you may have to delete blk*.dat to rediscover your own transactions during the redownload.
I've only tested this moderately. You might not want to use this for a website server until it's had some more testing.