You're comparing a horse to a car. Both are two different things. One is a living animal that needs lots of attention and care, the other is just a car.
Horses are better off that now people aren't primarily using them as cars.
If you don't know whether you're going to use an electronic on a daily, or even weekly basis, then you shouldn't be buying it. What's the point in having a $400 device sitting around that never gets used?
The OP already has both an iPhone 5 and MacBook Pro, and the Retina version at that. If he bought the iPad, he would either use the iPad more, or he would, again, have a $400 device sitting around doing nothing. So it's a bad move either way.
So yes, I'm still going to say to the OP that you shouldn't buy any of the iPads. Wait until the next update and buy some apps in the Mac App Store in the meantime and get some good use out of your MacBook Pro.