It's not worth it as an upgrade, especially for those who have the early 2013 models. Haswell is just a battery saving feature, there is no CPU boost. The main difference here is the SSD speed.
Like my iPad, I'm still using the iPad 3 (when it came out), I didn't upgrade it to the iPad 4, it may have better specs, but I could browse and watch movies just fine. For computers, if you actually needed all the extra power you could, you would have already bought one or bought a desktop with real computing/graphic power.
Now, with that said, I recently sold my mid 2009 Macbook Pro non-retina and I'm getting in on this update as my first Retina notebook. I plan to replace my iPad 3 with the iPad mini with Retina, which has the same pixel density as the iPhone, 326 ppi. I skipped the first iPad mini because I have no plans on going back to the old-school display. It's a practical upgrade, I get the same resolution, better pixel density, smaller size for me to carry around daily, and they both have essentially the same specs (Air and mini 2 with Retina), both have the A7 chip, same camera specs, etc.
I was really happy about the recent MBA update and almost bought it, every upgrade was welcomed, except it still use the old display. So I continued to wait for a rMBP update, since at that time (May 2013), it was mid-cycle. I know of the rumors that the MBA may get retina. Whether that's true or not, the rMBP is already thin and powerful enough that I don't need to wait any longer.
If there is no computing power improvements that you need, then it's not worth it. From a "showing off" stand-point, there is no physical difference between the updated models and the previous, except slightly thinner (.71 vs .75) but no one is going to notice it except you, if you notice it at all.
Looking at it from another perspective, if you add a $50,000 swimming pool in the back yard but it only adds $20,000 in value to the house, you've basically bought a $30,000 babysitter. Your money is better spent elsewhere.
