After reading the OP, I'm biting my tongue so hard it's starting to bleed.
The following recommended accessories will not prevent valuables left in plain sight from being stolen. I agree with the previous posts that covered that. However, these will help with regards to vehicle theft, carjacking, joyrides, etc. (This is the most constructive response I could post without starting an enormous flamewar resulting in bannination.)
- Ravelco. Thieves would need to tow the car in order to steal it. (Other threads here discuss it, just do a search).
- Escort Entourage C.I.S. (IMNSHO, better than LoJack; also 30% off the list price at Amazon).
Glad to hear your Z wasn't touched. I wish you well.