i was thinking to buy a new imac, as my 2012 or 2013 quad core mac mini is soo slow sometimes...

the processing in my mac mini doesnt seem to be the issue, however folder browsing speeds, loading times and other basic computer functions seem very slow.
It has 1TB of storage and of that is around 50% full.
My question is, could it be a worthwhile upgrade to buy a new external ssd drive and store most of the things (sound libraries etc) on there and use the mac mini only for the apps...
or buy a new imac?
Obviously buying a new imac is an easier option , (bar installing all my vsts and jumping thru some registration hoops here and there) but could upgrading the right components or buying a few specific items give me a substantial boost?