It's another attack vector, on top of all the existing attack vectors.
The attack vector these electronics close is hotwiring under the dash. This kind of attack doesn't happen as much as you think. More likely, people go for the GPS unit or something other item that's left out in the open, or your wheels and other easily-accessible parts. Stealing whole cars is rarer, unless you've got some collector's piece, and stealing whole cars via hotwiring is very rare. For stealing whole cars, there's a lot of low-hanging fruit, namely people who forget to lock their doors, people who more than crack their windows, or people who habitually keep the keys inside their car. And people who do steal whole cars for a living (usually for getting to less-accessible but more expensive parts) will have the equipment to be able to gain entry anyway, so it hardly matters.
The additional electronic security may close one or two attack vectors, but it doesn't close all of them, and certainly not the most important ones. So now the question becomes, is closing the one or two attack vectors worth the additional (literally) thousands of dollars worth of electronics as well as introducing an additional unknown quantity of electronic attack vectors?