Peter,
The topic of heat transfer is not a simple one even for us engineers. So it is hard to say whether or not you will need heat protection for your brake lines. But let me expand a little on why I went with a heat sleeve.
This Wikipedia article on heat transfer is a little technical and not particularly easy to read:
click here. But it points out that heat can be transferred from one object to another through three means. Conduction occurs when the two objects touch each other. I assume your brake lines will not touch your exhaust pipes. Convection occurs when heat from the first object is transferred to an intermediate material (e.g., air) and then to the second object. It is likely that air heated by your exhaust will carry heat to your brake line, but it is unlikely that it will carry enough to cause the brake fluid to boil, IMHO. The third method of heat transfer is radiation. That is the heat you can feel with your skin when you get close to an incandescent light bulb or a burning fire. This is the heat transfer I was most concerned about. While running hard at the track, exhaust pipes can get very hot and produce a lot of radiated heat.
The advantage of the heat sleeve is that it limits both convection and radiation heat transfer. Hot air cannot travel though the foil sleeve to reach the brake line, and much of the radiated heat reflects back off the foil. These effects are best if the sleeve is large enough to fit loosely and leave an air pocket between it and the brake line.
I've not heard of a problem with condensation causing corrosion of the brake line, but I suppose it could happen under some circumstances. One solution to that problem is to use stainless steel brake line.