Actually, at higher altitude, you have shorter boil times, because the boiling point of water is lower the higher you go. If you cook rather than rehydrate dried food in a cozy, there will be slightly longer cooking times. Since I just bring water to a boil, add it to my dehydrated meal, wrap it up to keep it warm, and let it sit about 15-20 minutes, I haven't noticed any difference in fuel consumption due to altitude.

If you and your friends are each doing their own meals, no problems. If you are sharing, that could be an issue. I personally could not go more than a day or two with just snack foods. As with everything else, YMMV!