My opinion, for what it's worth (which is next to nothing
), is that this whole soldering the connections thing is superstition.
The resistance of a good connector is less than the cable that it replaces so the only way that it can reduce the performance is if it means you have to put extra cable in. I think if you're careful then it should be just as good. I bet if you did a controlled, scientific test then it'd show that there was no measurable difference.
As for big cars. Well, it's true that you need a spanner to take off the battery leads. But big cars have fuses! That's why your car doesn't catch fire when you short out the radio
.
Just my two penneth ...