Personally I go with the theory that prevention is better than cure. I also wouldn't want it back if it got stolen.
With that in mind, to deter the thieves who don't want confrontation then a Disklok is a must, and if you have Keyless then you'll want a faraday pouch to stop the 'relay theft' thieves:
http://amzn.to/2v3HTN2 It's not widely advertised/known, but you can switch the keyless function off. Lock the car with the fob, then within 5 seconds press the keyless button/sensor on the door handle. That switches off the keyless-entry system until the next time you unlock the car with the fob. Perfect for when leaving the car overnight or if in a particularly vulnerable place.
One thing people forget is their house is also a target, so get any Euro locks replaced with anti-snap locks, get sash-jammers if you have sash windows etc etc.
IMO, trackers are pointless unless a) the insurance company insist on one and/or b) it's installed in an unknown place. However due to there being very limited places to install, they tend to be found very quickly and ripped out. If it's not needed by your insurance company then I wouldn't bother.
Some people say the Ghost is a good alternative, but I've read stories about Ghosts kicking in and the owner being dragged outside for the code.
A lot will also depend on your personal circumstances. For example if you have kids you'll not want thieves coming in the house, whereas you might be a bit more relaxed about that risk if you live on your own.
Remember though, if they REALLY want it they will take it whatever you do, so your choices should be made based on your approach to risk.
HTH
