What you have to always remember is that all security buys you is time.
If someone's determined to nick a bike (or anything else) they will, so the only thing you can do is to make the potential profits not worth their time.
I know someone who doesn't care too much about the cosmetic state of their bike since, especially if it's standing next to a pristine bike, the scrotes will go for the one that looks better as they'd be able to get more money for it.