This is an interesting topic, I wish there was more discussion about it, thanks for your thoughts and assessment. I'm with you, I don't think Apple will double the resolution of the mini to be the same as the iPad 4 for a few reasons, one of which is that I've not seen compelling evidence that they could do so technically without turning the mini into a pregnant or fat mini, which would run contrary to how we see the mini today, as thin and lightweight, an excellent form factor.
The other reason, which is I think a bigger reason is that the full sized iPad (4) is their premium product, the one that makes them more money, the one they will always want people to buy, the one they will pack with more features and functionality to entice people to buy and spend more money with Apple. If suddenly all the same functionality and features were to be included in the mini, the full sized iPad would lose some of its "compelling" aspect and it's logical to conclude sales of the premium iPad would suffer. It'd be like including cellular technology in the iPod Touch - suddenly the iPhone isn't differentiated enough from the iPod Touch, and its premium price tag would look odd.
Proper product strategy in a business requires strong and clear product differentiation (something at which Apple excels), and unless Apple moves to "size" as the differentiating factor in this device line (a strange factor on which to differentiate only), a doubling of the resolution in the mini is highly unlikely (today - perhaps the iPad gets a resolution bump in the future?).
