To be honest it's still a pretty neat PC. An SSD, additional 8gb ram and the extra monitor and you would be good to go. Would run you in about 280$.
If you got the money and want an higher end flashy system.
https://pcpartpicker.com/list/Bx6KxYWould look a bit similar to my PC in my profile.
I can also recommend the nzxt s330 case for 60$ it's similar to my case and has a very clean stylish design.
If picked another 1tb hdd, you could reuse the old one. But I think it would be easier to sell it as a whole PC. Would get a few hundred.