On its face I agree that when an alignment is performed that it's important that the output of the steering angle sensor is properly calibrated to reflect the actual steering angle of the wheels. That's important for the electronic stability control to be able to do its job.
But the same applies to the old school version of the steering angle sensor (the wheel in front of the driver) and yaw control (driver inputs). Go out and get a bad alignment and your wheel will be off center as you go down a straight road. You can adjust to that, but the computer will wonder what's going on; steering says we're going in a circle, but wheel speed says we're going straight. If the discrepancy is slight, then the computer will think there's a lot of slip angle happening between the wheel/tire/surface of the road (something it has to account for anyway). If things are too badly out of whack a threshold will be crossed where ABS and stability control functions will be compromised so badly that warning lights will start flashing (at that point you will have long since noticed your crooked steering wheel).
I assume that a modern electric steering system works in much the same way as a conventional one. That is, there's a sensor on the steering column that goes to a "rack" and then there's either a motor for both wheels or a motor for each wheel to independently control ackerman angle. Either way, the toe adjustment is made at a tie rod end between the motor and the wheel. There's no adjustment ever made between the motor(s) and the angle sensor. So you can't screw that up, right? The only advantage to using Volvo's vida is that you can read the zero position of the wheels based on the motors and the sensor. This gives you a perfect starting point for your alignment and also would flag any wear in the system between the those parts.
So...if my assumptions are correct then I believe the answer to your question 2 is yes, you can get your alignment done at a good independent shop. That would be my advice for the following reasons:
1. Your 30k mile car is unlikely to need any significant adjustment.
2. A good alignment tech isn't going to screw it up so bad as to make difference in the performance of the car.
3. There has got to be better tire options out there, ones that will last more than 30k miles.
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