carapace armor has it's merits, because there is an amazing overabundence of ap5 crap floating around. However, it has to then be given to the WHOLE army, which gets expensive, fast. I prefer to be armored in numbers.
The best way to use carapace armor would be on Rough Riders or Xeno Mounts, because unlike the rest of your army it SHOULD be in close combat and it's cheapest to do it like that. Also, if you combine carapace and xeno mounts, you've got Guardsmen with the equivilant of power armor. I don't imagine people playing guardsmen usually think to bring a lot of power weapons or ap3 guns, so they may be in for a nasty surprise.
I don't like cameleoline either, because that would require me to hug cover, where people could just run up and flame the crap out of me. Also, that requires either infiltrating into cover or walking in there, and I don't like the idea of guard platoons getting closer to the enemy then they really have to. I would rather just not spend any points on those upgrades so I can get continously more guards. Guardsmen win battles, not their saves.