Every iOS update slows it down more and more and makes apps crash more as they run out of RAM and developers have only tested it with the latest device.
The original iPad was very much sold on the promise of upcoming third-party apps. If it didn't have the potential of apps, I would definitely not have bought it, just how I didn't buy the original iPhone.
I have a first generation iPad and it does more things than the first day it was purchased.
Not being updated will mean that it will do the same things it does now but no more. That's far from junk.