I have no experience with either Sandy Bridge or Ivy Bridge. Everything I have with 16.0 on it is either a little or more newer, or older. The older is 2 Intel CPU generations older, 2010 with Ironlake i5-660 using the Gen5 on-CPU GPU. Both Terascale 2 GPUs I have are coupled with CPUs that don’t support Leap 16. So, I cannot comment based on direct experience, but I do have a pair of generation subsequent to Ivy Bridge Haswells using Intel Gen7 graphics that seem plenty spunky with 16G or more RAM. Note however I’ve nearly eradicated Plasma here, only a small handful of installations on newer hardware. Everything else is running KDE3 and/or TDE.
All that said, I can’t imagine Plasma being the slug described in OP, unless it was hamstrung by having been installed using the nomodeset kernel cmdline option that wasn’t removed post-installation. Historically that’s been a common problem readily fixed if recognized.
Traditionally, Dell cases haven’t been very accommodating to generic motherboards, but I’ve seen a number of the “newer” ones really are generic enough for mATX motherboards as long as the cables from the front panel switches and sockets are close enough to generic to make work. Front USB cables generally are standard enough, but the PC speaker, power switch and some others can be frustrating. IIRC, Vostros may be one such model line, but I can’t swear to it. Genuine generic cases have separate plastic connectors per purpose, usually with two wire connectors each for those various bits, while brand name cases, “generic” or not, couple sometimes 11 or more connectors that must be removed from their original plastic and connected one by one to a generic motherboard, a tedious job even if old eyes are good enough to deal with mousetype .pdf manuals and motherboard connector stencils.
I would give your current Vostro another try with 16.0 before spending money on newer hardware, unless you know neither nomodeset nor some uncommon but fixable old radeon problem were handicapping you.
As @malcolmlewis suggested, it might be worth comparing your Terascale GPU to your CPU’s GPU (if it actually has one - look up your CPU model on intel.com to confirm). Run glmark2 to get a simple number to compare to running it again after removing it. Assuming the Vostro has the HDMI connection you need for your Samsung, the CPU’s GPU should work automatically, as long as kernel-firmware-i915 is installed and no override configuration(s) is in place for the removed Terascale.
Then again, off-lease computers can be a really good value. I still have Dell SFF Optiplex 760 and 780 models from 2008 I bought as “refurbs” still working well enough with 15.6, Tumbleweed, Debian, Mageia, Fedora and *buntu. That seems to suggest today’s “refurbs” ought to be good for 8-10 years or more.