Legacy is just referring to older versions of the Mac OS. If you're not running a newer version then you can come up against issues with newer Apple tech, like the latest versions of iOS and newer phones. My iPhone was essentially bricked when I updated to iOS 10. It was incompatible with my older version of the Mac OS and iTunes. No way to restore or anything, until I was able to update to a newer machine.Thank you for responding. i would appreciate knowing what you mean by legacy?
I would suggest that a new iMac would be a better option, as you may have only 1 year or less with your 08 iMac working.
Add to that that parts are difficult to get unless you find second hand iMacs, you would be best off with a new iMac.
If you want to keep using old software on a new iMac, you can use VMware fusion or parallels to hold an older mac system inside your current mac.
If all you need is "storage space", just buy a USB3 external drive and be done with it...
OP's not going to get USB3 out of an '08 iMac.
I think I'd be mildly inclined to replace this machine rather than upgrade it. It wouldn't be all that hard to change out the hard disk for a newer / larger capacity one, and it wouldn't cost all that much. I don't know how hard a job it is, if it's anything like the early '09's it's tedious and fiddly but not intrinsically difficult. However once you do that you're still limited to a max of I think 6 Gb ram, and El Cap (supposedly Sierra will run with some fooling around).
If you just need a few more months, the hard disk upgrade is definitely an option. Or, an outboard USB disk to relieve the immediate storage problem, but it will be slow since you're limited to USB 2.
You might look for a refurb or gently used "late 2015" iMac, which will be a significant improvement over your current machine and ought to be cheaper than brand new.