I'm in a somewhat similar boat, I have a 21" iMac 2010 with the 3.2GHz CPU, 4 GB RAM. I might replace my internal HD to a 512 GB Samsung 850 EVO, and the 4 x 1 GB to 2x4 + 2x1 = 10 GB
I'm sure this will be second life for the iMac, as the CPU is still very nice...
Either that OR waiting for Rev 2 RiMac with (hopefully) a decent GPU and less heat/noise
I'm still undecided and shoveling this idea around my brain's corners
oh well
If you upgrade this yourself, take caution to reattach the Temp sensor for the drive correctly, or your iMac will surprise you with eternal max fan speed noise
, or so I heard
. there are a number of imac upgrade experience threads here, it might be worth to quickly scan through them
Good luck and tell us of your success or experience