I've created a few offline wallet.dat files back in summer of 2011. I've been adding coins to them (through pools) since then but I've never used them online with any bitcoin clients.
Am I safe? Am I able to access the coins later on for use? Or should I be regularly resyncing the wallets, even if I'm not spending the coins?
The Bitcoin client back then didn't have passphrase encryption, so that means you want to be very careful with that wallet.dat.
Some might suggest using an offline computer and bringing over a more recent Bitcoin-Qt client to do the passphrase encryption before taking that wallet.dat over to another, connected computer.
Or to use Armory on the offline computer which provides a secure method for spending.