8-16 RAM update worth it?
Only you can answer the question as to whether an upgrade is worth it or not, but I do have some observations to make.

Firstly, your mid-2012 13" MBP doesn't actually meet the system requirements in terms of GPU. The page you reference specifies the following GPU requirements for macOS:


  Intel Iris Pro Graphics (MacBook Pro 13'' or 15'' mid-2015)
  Recommended: Dedicated GPU like AMD Radeon R9 M370X or better
  Minimum Video RAM: 4 GB RAM


That is, the minimum is a 13" MBP from 2015 and yours is from mid-2012. This implies as a minimum you'd need an Intel Iris Pro 5200, not the 4000 series you have. The 13" early-2015 model you have that works better has the Intel HD Graphics 6100 which can use up to 1.5GB of your RAM.

The second observation is that the specs of your mid-2012 MBP's GPU is that it can only use up to 1GB of RAM, not the 1,536MB you specify in your question. 

So, while I'm a big believer in having more RAM, in this case for this specific purpose it's probably not going to add much life to this machine. Sure, it's worth doing for other uses (especially since the Intel HD Graphics 4000 uses up to 1GB of your MBP's RAM for its VRAM, so having more is going to be useful when running multiple apps simultaneously), but the benefit you'll get with Gopro Fusion Studio to render 5.2k content is questionable since you don't meet the minimum GPU specs anyway.