I think its great, one of my biggest gripes about the 2010 version was the overabundance of nearly every metal you could possibly need. I could pick any given embark at random and odds were good I could outfit my dwarves with as much steel as I wanted without having to trade, this was lame IMO and made the game predictable and easy.
Now sure, you can use self-limiting tactics, but I prefer it this way as I have to go in with more unknowns. "How much metal will there be? What kind will it be? Will there be coal?", these make me have to adapt my play style, not just rely on the same thing over and over, or use self-limiting which is nice but you still know exactly what you are going in with.
I also like how your parent civ has to have the necessary metal for you to embark with, so sometimes you don't get everything you'd want.. That said there does appear to be a bug where they can have steel but not iron, or bronze without copper, etc which can be a hassle.
I'm not saying there aren't some things that need hammered out, but moving to low resources instead of easier mode high resources (sorry to those who find the term insulting but I don't know what else to call going from resources being rare to them being literally everywhere in every map to the point that digging in a line downward towards magma has me go through several metal veins just by chance) is a good one and makes the game far deeper, more complex (in the sense you have to adapt your strategy) and of course, fun.
Lastly, yes I do think that getting the full caravan arc will make the rarity in metals more balanced.. However keep in mind Toady chose to release this in parts instead of one huge one waaay down the line. This is good for us as we get to experience some of the updates sooner rather then later, and good for him as his legion of beta (alpha I guess..) testers can look for bugs on individual parts.. However the obvious flaw will be its going in piecemeal. If people don't like that they can always use 31.18, its not like its gone or anything, and wait until things reach a point they like to upgrade.
-MB