How often do you track? enough to justify a $1000 cage? likely no.
Do you track hard enough to worry about rolling over your daily driver? likely no, or at least I would hope no. they cars will not roll over easy, and a track is really the last place for a car to roll. (lot of factors Mazda Raceway maybe, PIR not a chance.)
I track the car a couple days a month during the Spring/Summer/Fall (15 days this season) and at tracks with speeds of up to 120 MPH. Of course my car isn't going to roll over like an SUV due to turning too sharply; however, when you get off into the dirt, anything can happen and it's certainly possible for a tire/wheel to dig in and cause the car to flip. Now would I be better off with a separate purpose built, fully-caged race car, absolutely, and now that I've gotten into this so much I'll likely move to that in another year or two, but for now I'm really enjoying the ST and it's worked out great as a DD/Track Car. Also, my short 1.5 mile commute allows me to compromise DD comfort for a bit more track capability than others might tolerate.
Do you daily the car? assuming yes. do you wear a helmet? Assuming you are doing something stupid enough to need a cage and roll your car during your daily or back road driving? you would be worse off with a cage in the car... why, because cages REQUIRE a helmet. if you smack your head on one of those bar you will be worse off than not having it.
I do daily the car, which is why a bolt in roll BAR is an attractive option as it can be relatively easily removed when not needed. As for hitting your head, I fully agree that a helmet is best, but just as @03threefiftyz alluded to, the part you normally hit your head on is the halo that would follow the top of the door frame in a car with a full CAGE. My neck would be in some serious trouble if my head managed to go around to either side of the head rest and smack the bars behind the seat.
lastly HAVE YOU SEE THE A-PILLAR IN THESE CARS???? they are HUGE!!!!! the likely hood of you needing a cage isn't very high in less you are running way over this cars capabilities.
The A and more likely related to a roll bar B pillar in the car do look beefy and I hope you're right that they will hold up well in the event of a rollover. Even with the roll bar I'm still relying on the A-pillar to hold up the front part of the car, but the B-pillar/roll bar area is more critical as the roof is only an inch or two from the top of my helmet, especially since I'm running Schroth Quick Fit Pro harnesses. The harness bar aspect will also improve the angle of the Quick Fit harnesses making them a little safer.
The rare case you might need it. if you have a 2.3 with huge turbo and making 550-600 wHP (with all other supporting mods to the rest of the chassis) and you are out pushing the car as hard as it will go and beyond your limits and you roll... and I mean roll hard enough at this point to need a cage, the car rolling over once or twice even doesn't need a cage. A car that has the ability to roll over 4-6 times, yeah then yes.
The car totally stock is plenty capable of both straight line and especially cornering speeds where there is rollover danger (again from going off track).
Just my thought. I have seen lots of pictures of these cars on their tops and not one looked like it needed a cage.
I'm glad to hear that and hope I never have to test out the roof of the car with or without a bar, but for me $1k is cheap to improve safety even a little bit.
If you track the car and do not ever drive it without a helmet.... I would recommend a cage! daily driving a caged car is stupid of you and anyone of the passengers in the car.
oh and don't even tell me you can put padding on the bars to make them safe... "safer" yes but not safe. Padding is to lower the blow to the helmet but the caged car would still require a helmet.
. 
