A monitor is very cool but definitely a theft magnet for already overly popular cars to steal....

But seriously though, it depends on you...

If your car is constantly parked in places that you don't feel that great about now, then I would just get over it and move on because having an addition $1G in car video stuff ain't gonna make you feel any better leaving your car parked there. Also, will your current alarm be good enough to protect these additional toys??? For me, if I put in a DVD player and screen, I'd want to have a whole bunch more features on my alarm like motion sensors outside, paging, etc... And like you said, would you seriously spend over an hour just sitting in your car to watch a movie??? Mostly likely not.... These items to me are like body kits and big rims - more for show only....

Again though, its your call....