For everyone's edification, here are the dry/wet boiling point specifications for the different brake fluids:
Dry boiling point Wet boiling point
DOT 3 205 °C (401 °F) 140 °C (284 °F)
DOT 4 230 °C (446 °F) 155 °C (311 °F)
DOT 5 260 °C (500 °F) 180 °C (356 °F)
DOT 5.1 260 °C (500 °F) 180 °C (356 °F)
Why would I want to change over to DOT5 if that much work is involved?
With the advent of DOT5.1, you probably would not want to switch over. One of the major disadvantages of DOT5 is it doesn't work with anti-lock braking systems. If you want to remove this part of your braking system when doing the change over, then you'd be okay. If you do not fully clean your braking system with solvents while switching over, the DOT5 will be contaminated and will not function as expected.
Also, if there is water left in the system during the switch over, the water will pool or "puddle" within the braking system which can cause corrosion. If that pool or puddle of water just happens to be in your caliper (or winds up there), it can flash over to steam if the environment gets hot enough, which can cause you all kinds of issues (back flow of brake fluid out of the system; complete loss of braking). This makes it very important to get all of the water out of the system when using DOT5.
Are the benefits that huge where I would be motivated to do this?
This question is very subjective, but for the most part, no. With DOT5.1 available, there really aren't huge benefits for moving to DOT5.
What are the applications and benefits to DOT5 brake fluid?
As vini_i stated, DOT5 doesn't absorb water like DOT3/4/5.1, so that is a major plus factor for it. DOT 5 has a service temperature range of -55°C (-67°F) to 55°C (131°F). It is used exclusively by the US Military for this reason. If you live in the Yukon Territories (Canada) or Norther Alaska (US), you may have an argument for using DOT5. DOT5 is also specified for some Harley Davidson motorcycles (though I understand they have stopped specifying it for their later models).
Additionally I have seen references to DOT5.1?
As alluded to previously, DOT5.1 is Glycol Ether/Borate Ester based just like DOT3/4. This makes them compatible, unlike DOT5 (which is silicone based). DOT5.1 has the same Wet/Dry boiling point specification as DOT5 as well. It will work with antilock braking systems, just like DOT3/4. Plus, you don't have to do any major disassemble of the braking system to switch over to it (as long as your braking system doesn't call for DOT5 or it wasn't previously converted over to DOT5).