- Bar end shifters are cheap and reliable. If you read the threads in this forum, these qualities are important for many tourers.
- They allow for friction shifting of the front derailleur. This is important, especially with the big cassettes that so many people use. Touring bikes tend to get less well tuned during a tour and friction shifting allows you to remedy a chain rattling against the cage quickly. I consider this a huge blessing. Campagnolo brifters have something similar to friction shifting as I understand, so I expect they are more helpful than Shimano brifters. Repeating Sheldon Brown again: "Rear indexing good, front indexing bad".
- If you put your bike against a wall and it is very heavy, pressure against the brake lever might cause a shimano brifter to shift. This is less likely to happen with a bar end shifter (or campagnolo).
- I find that being able to shift many gears is an advantage that pays off for tourers. If you're in the completely wrong gear at the foot of the climb, it is easier to correct this with bar end shifters.

On the other hand, a lot of the advantages of brifters are reduced when touring because you're leisurely riding a very heavy bike. Brifters are made for racing, to respond quickly and dextrously. If you find yourself having to shift five gears quickly, it's your racing that is the problem, not the equipment. Brifters look good on racing bikes, but touring bikes are rarely beautiful as a whole. You're much more likely to find yourself having to shift while keeping a tight turn during a race than during a loaded tour. Deep in a peloton, a slight wobble can send the whole bunch sprawling, making the ability to shift while keeping your hands on the handlebar much more useful.

I found the suggestion to 'just take along a pair of downtube shifters' to be rather funny. For me, shifters don't fall in the category of things I want to take along as spare parts. In addition, if I have to change them, I will want to do so in my shed, not by the side of the road. But at the same time I wouldn't expect brifters to break down too easily, so for most tours that will probably not be the most important consideration.

But for all these reasons, I consider brifters to be an acquired taste rather than offering a real net advantage. They are certainly not useless and I can readily see why someone would prefer them; coolness factor plays perhaps a stronger role than some are willing to admit. And why not? Having a bike I love is of utmost importance to me, so I would certainly spend the money for brifters if I simply felt I wanted them. A tourer spends a lot of time on the bike; feeling good about that bike, for whatever reason, should be an important factor.

Remember to keep enough money for food and lodging though.