Exactly. I think setting a limit like no more than 12 registered accounts from one IP address would be enough to not worry about abusers ever more. Or am I missing something?
IP limitation was never a good option to prevent abuse of any sort. Using VPN or any kind of proxy will defectively render this security feature useless.
If the faucet farming is really that harmful to the site then the best way to prevent faucet abuse is to limit faucet somehow.
For example: Faucet should only generate really low amount of satoshis, and grow over time with more wagered BTC.