If the Aura HD is still working and you are happy with it, then it probably isn't worthwhile upgrading to the Aura H2O E2. Unless you need a waterproof ereader. You lose the SD slot, but get more internal memory. How important that is depends on the number and size of books you read. The performance should be the same. The only other thing you might really notice is the new front light.
An upgrade to the Aura ONE is a bit different as the extra size might be something you want. Plus it is the only device with the full Overdrive support. All the other factors are the same as for the Aura H2O E2.
Of course, if the real point of the question is that you want a new toy, then do it
Go for the Aura ONE. Keep the Aura HD if you need something a little more portable.
As to the page turning problems you have seen, that does sound like a firmware problem. I seem to remember that happening a while ago. It only lasted for one or two versions. Did you put off upgrading the firmware for a while?