Flash the newer version of ROM over the old one on ART environment I've flashed Carbon ROM on my LG G2 (D802) device and when e new Nightly release, I download it and put it on my SD Card and dirty flash it (Only clean Dalvik cache and cache partition). Now I've changed my enviroment from Dalvik ro ART and it seems that everything except nandroid manager is working fine, my question is, when a new Nightly release, what should I do now exactly? should I dirty flash like the other ones? and when I flashed the latest Nightly, what will happen to my environment, will it change back to Dalvik or it will stay on ART environment? 

Thanks in advance.
It should be identical to flashing when Dalvik is enabled. If the ROM cook packaged up everything correctly, you should be able to "dirty-flash" the nightly builds over the previous ones (assuming you are staying on the same ROM channel.)  I would confirm with the ROM author though.

On the topic of wiping caches, the CyanogenMod's installation instructions specifically state:


  Contrary to popular belief, there is no need to wipe ANYTHING when you
  update CM. This includes your cache partition, your dalvik cache, and
  your battery stats. While wiping these won’t hurt anything, you can
  increase the time it takes to boot up CM after you install the update.
  Android is smart enough to manage both your cache and dalvik cache
  without you intervening, and wiping your battery stats does absolutely
  nothing to help with your battery life (the file is only used to
  provide the raw information to provide the stats and graph in Settings
  -> Battery) – it is actually wiped automatically every time your device is charged to 100%.


Of course you should always have a recent backup via recovery in case things start to go wrong.