Blacklists will only do one thing, grow and grow and grow; if they grow large enough, your site speed can take a hit and they become very hard to manage. The key is to use whitelists. You block everything from your site; then you allow only what you want to come through. Bots keep changing daily and bad bots ignore robots.txt files. Block one bad bot today and two will take its place tomorrow. If you block all the bots and only allow the ones you wish through, it makes it a whole lot easier to manage.