I'm down with metallic dragons being unaligned. I like the idea that metallic dragons can do good in the world while still being greedy, selfish, slothful, eccentric, single-minded, or perhaps just bad tempered.
Unaligned just makes it even easier for a DM to say this particular monster is an enemy or ally (beyond the simple fact that DMs can do anything already). Look at the alignment and flavor text and its easy to come up with ideas about how a group of PCs could both cooperate or come into conflict with a metallic dragon. This increases the monster's versatility in adventure design and makes them far more than an enemy - something far more dynamic. To make them Good would be just like making them Evil only placed at the opposite end of the specturm. Unaligned provides DMs with the maximum range of options when fitting metallic dragons into their adventures. For some reason a lot of people equate Unaligned with Enemy. Funny, that.
I apologize for all grammatical arrears.
I also like the idea of unaligned metallic dragons, but for different reasons. When a D&D Dragon acts there actions come off as very cat like to me. That Is to say that if I took a real world house cat gave it intelligence and made it bigger it would act exactly like a dragon. A metallic dragon is still a dragon in other words a big carnivore, so most small, medium and large creatures fit right into there prey range. Sense all PC's are in this range dragons will often see the players as food. Regardless of being good or evil everything needs to eat, and this is where I see the first cat like quality. Playing with one's food.
For evil play which is often associated with chaotic alignments, a dragon could cause it's prey pain or scare it into a panic for fun. For unaligned play a dragon could have a conversation with it's prey or give it a chance to live if it could solve a riddle. The good alignments have a hard time applying to feeding dragons, because there's not much to eat. If your a good dragon you don't want to eat sentient beings because thats "evil", and you don't want to (but can) steal and eat heard animals. This leaves you with only a few options that won't fight back to the point that the risk is to high for the reward.
The second cat like trait is greed. No mater what alignment a dragon is they amass far more wealth then they need or could by normal means. For evil dragons this is easily explainable as theft. For good dragons the only explanations are payments and favors. A favor being ether something given to the dragon as a reward or as a gift. In the first case a dragon could steal or ransom ungodly wealth in a few months. In the second more honorable manner a dragon would have to spend several years collecting to have a decent hoard. In general dragons usually accumulate their hordes in an unaligned manner utilizing all these methods and others.
Other traits like pride and sloth can be found in all dragons. Metallic dragons don't go out of their way to help the "lesser races", and chromatic dragons usually only destroy those who stumble into their layers or look tasty. For being generally uninterested in others I'd say they are unaligned.
As for a cats vanity tell me you've never had a dragon lick it's claws clean instead of just taking a bath in a lake. Vanity for a dragon is having a bigger nicer and more lavishly decorated layer. nothing inherently evil about that but I don't see it as a good action ether.
Metallic dragons and chromatic dragons are separated by the frequency of evil and good actions. Chromatics generally like to see their food squirm more and they have a problem with delayed gratification. On the other hand metallics are calm and if it dose not cost them anything have no problem with someone else going first. It's the cruelty of chromatics that gets them labeled evil, but metallics just aren't like that. This makes metallics closer to being but not necessarily good.
As for equating unaligned with enemy, I thinks we do this because they are more dangerous. If a creature is good or evil I have some idea and sometimes a very good idea where they stand. With unaligned creatures I have far fewer clues and none of that information is as sturdy as it is with good or evil creatures.
