Time to upgrade
I currently have an iPad 2 16GB, which I managed to persuade work to buy for each of my team when it first came out (and which I bought from them for £80, when I left a couple of months ago), so it doesn't owe me anything.
I'm running a fresh (not restored from backup) install of iOS 7, which keeps me waiting occasionally, particularly on my chosen database app (MyStuff2). It now takes 5 to 7 seconds just to update a field in a record from a drop down lookup list, which means 15 to 30 seconds per record (for comparison, every update is of course instantaneous in Excel on a laptop). Swiping between MyStuff2 and Safari often results in MyStuff2 reloading entirely from scratch (another 10 seconds, then you have to find where you'd left off). I assume this is due to memory constraints - I often get the same issue when switching between tabs on Safari (incredibly annoying if you're filling in a form or posting on a forum and want to reference data from another tab). Safari also sometimes crashes when there's too much going on on one tab.
It's finally time for an upgrade, with a faster processor and more memory. "Disk" space hasn't really been an issue so far - I've still got 2GB+ left after all this time and I don't use it for music, as I use my iPhone 4 (a freebie replacement for my old iPhone 3G) for that. The only video I use is for offline viewing with Plex, which doesn't happen very often (planes and trains) and doesn't take up much space for a few TV show episodes. I know that 16GB won't be enough on a retina display, so I'll be going with iPad Air 32GB (Black Friday or refurb from Apple) or Air 2 64GB on Black Friday if I can wait. I'm also looking at getting a refurb (if Apple ever get more stock - other shops don't seem to realise / care that their refurb prices are now the brand new price from Apple) 16GB iPad Mini 2 for my mum (since the Mini 3 isn't an upgrade to the Mini 2, unless you want Touch ID).
I gave away my old iPhone 3G to my friend's 7 year old daughter. The battery still lasts ages with no SIM / wifi only and they save it as a special treat for long car journeys. I expect I'll do the same with the iPad 2 (at some point between her recent 8th birthday and Christmas), as she's wanted one ever since she saw mine (even though I'd just given her a laptop!)
The battery life, (which still qualifies as "remarkable" on my iPad 2, down slightly from my original assessment of "magical" when I first got it) portability and touch display are probably the reason most people seem to prefer a tablet these days, since the iPad came out - and got it right. I haven't been blown away by Apple's incremental upgrades, but Android never really felt right for me, so I'm sticking with Apple for now. Conversely, Apple's OSX doesn't float my boat (the hardware's nice though - and equivalent spec / quality PC's aren't really any cheaper - so I build my own) so I'll be sticking with Windows 8.1 on my PCs, then I guess Windows 10 (apparently 7 ate 9?)