Before buying my Z, I had an FJ Cruiser. I had the Viper 5904, with Viper SmartStart. The advantage of the Viper SmartStart module is, if you have an iPhone, Andriod, or even blackberry: You can MONITOR, unlock, lock, and remote start your car ( everything you can do with the remote. ) and more. The more is you can go into the Viper SmartStart app and mark the place where you left your car incase you go to an amusement park and need to find where you left your car.
You can also setup all kinds of alerts within the program. Such as speed limits, proximity alerts, ect. This would prove useful if you think the guys where you take your Z are taking your car out on a Ferris Bueler's Day-Off fueled joy ride, instead of diagnosing your car. Also, if the Z is now your DD.. you can tell by your phone if your Z is being taken by someone within your household while you are at work.
Only drawlback is that Viper SmartStart is about $15.00 per month. But that's a small price to pay for a peice of mind that you know exactly what your car is doing through your cell phone all the time.
Hope this helps. Take care
* Oh also the biggest benefit: ( Dont know how this would work exactly with the intelligent key ). But when I had my cruiser and I was going to an outing. I would leave my keys in my truck and only carry my cell phone with me and lock the car from there. I dont think you can really lock the car with the intelligent key inside.. not sure.