Assuming that they are parked and probably with the engine off during this time, what are the collision dangers, and do they warrant the cost of kit?

Also, I have air bags in my car and was hit by a another car coming out of a junction to the side. It was not very high speed (he was accelerating from a standing start and I was doing under 30) but, because of the angle, it was enough to twist the chassis and write my car off. However, the air bag was not deployed.

I know you can also turn off the airbag using the key. Your manual will guide you on this. You can then turn it back on again when the car is being driven.

Not sure if this is practical though, but I thought I would mention

Airbags will not deploy unless the vehicle is moving.

The drivers airbag cannot be de-activated. The passenger one can (when required) when rear facing child seats are used.