I'm using the secondary iMac today (as pictured - except I've gone all cordless) because the main one is still being fixed. It's still a lovely machine and was the main system for about four years.
The repair shop phoned with some interesting news. Apparently my broken 2012 iMac gets (Yippee) a free service replacement of the fusion drive.
My older iMac is from 2008 and I hadn't bothered to update it for El Capitan until now. It still works okay, although the disk is slow compared with the newer model. Curiously the whole machine is gradually speeding up as it sorts itself out, However, I'm thinking about a further upgrade of the innards for this one, to solid state disk.
It may sound bonkers, but I have a feeling that this more modest machine would get a new lease of life from such an update. I updated my Thinkpad with SSD ages ago and it was so much faster afterwards.
I've taken the 2008 iMac to bits once before. Interestingly, the older 3 cm thick iMacs are a lot more accessible than the newer 'thin' ones. The magnetic glass screen was a brilliant idea. So on the older machine, I think I could do the SSD change myself.
Not until after the other one returns though.