There are only two things the Mini is missing as compared to the updated 9" iPad, that being the use of the A6X processor, and a Retina display.
The Retina display by far is the most expensive component in a tablet, so I think it goes without saying that it wasn't going to be included in the first generation. As far as the A6 chip goes, sure, I would have like to have one, but coming from an iPad 2 and an iPhone 4S, I can tell you that the iPad mini will not suffer any performance issues.
So you don't get Retina, and you don't get the A6 processor, but you do get a $170 less price point. All things considered, I think it's a fair deal. Granted, I would have been happier had they stuck at $299, but I understand why they went with $329 given the price point of the iPod touch.