I have a 64GB iPad 4 that I've owned for 18 months. I was delighted with it while running iOS 6. Due to various security bugs in iOS I was forced to upgrade to 7. I'm not so delighted any more. There are lags and pauses that are a distraction. And there's no way to go back.
I've owned an iPad since gen-1, day-1. (skipped the 3) I will continue to use my current iPad while keeping an eye on what Apple does over the next 6-12 months. I see little sense in buying a tablet made of "premium material" that will physically long outlive it's functional usefulness.
If I'm to buy another one, Apple is going to have to show me that it will protect my investment... and forcing updates to the OS is not my idea of protecting my investment.