In my experience, low end blues no, high end blues yes.
It depends of course on your server and the prices. But, there's usually a flood of low end mats (e.g., Small and Large Glimmering shards) and not a lot of demand. At the other end, Large Brilliant and Large Prismatic are in demand, but supply is more limited. If you can find cheap enough blues that DE into the Large Brilliant and Large Prismatic, then it can definitely be worth it. However, there are almost always a number of other enchanters out there looking for the very same deals. So, don't expect to corner the market on it. But, incorporating it into your AH routine can be worth it.