No matter what the parking situation in NYC is, it's a HUGE mistake to give someone you don't trust the keys to your Mercedes.
Buy an old Honda for driving to where the risk is as high as you described. Judging by your site and car list, money flows like water in your neck of the woods. Buy another car for valet parking situations. If the image of bringing your E55 is too important to you, then you'll have to live with it being stolen.
The Lojack system is being duplicated by Teleaid, OnStar, etc. If you subscribe to Teleaid, don't bother with Lojack.
Who would know that the parking garage attended didn't question the validity of it.
He makes minimum wage and couldn't give a rat's ass about some schmuck's Mercedes. He's not paid to care, just to stand there.
I used to be in the auto security biz, and don't have much sympathy. Owner precaution is 90% of the game, hardware the other 10%.
Years ago I was checking into a hotel that indicated that owners would not be allowed to park their cars. Valet parking only. When I balked, the valet pointed to the row of MB's and other luxury cars to be parked, and explained that THOSE owners (of more expensive cars than mine) let their cars be parked. I told him that they must be much wealthier than me, as I could not afford to lose my car.
After a discussion with the hotel manager, I parked my own car.
Mercedes engineers spent time, effort, and our money (in the price) in designing the SmartKey. It's the best anti-theft key on the market, bar none. You completely give up all it's protection when you hand it over to someone.
Some insurance companies have stopped paying on theft claims where the owner either valet parked the car, or left it running while they ran into some place. I hate to side with insurance companies, but I don't want to pay higher premiums for sheer stupidity.
1998 C230 "Black Betty"