Cycles vs internal vs game engine Trying to discover why the Blender Internal and Blender Game Engine Renders seem to be generally thought of as that different for rendering from a quality perspective.  The perception of a difference of quality appears to be what the popular understanding of many users would to indicate.

Is there really a qualitative difference or is it mostly just the same render engine?  My understanding is that Game has a sort of live time render to it, and that Cycles is the newer upgraded render machine and also that Cycles is primarily for photo-realistic and fancy node based effects stuff.

Are there any outside plugins or texturing programs possibly that aid or add significant upgrades to the render engines that are commonly used in workflows that might aid in this perception?

It would seem that Internal and Game Engine seem to be at this point just minor, rough, or quick model and scene color fills for the most part or maybe used for a quick rough tests for pre-Cycles renderings? Agree, disagree?
Besides what is stated in the linked question about the differences between Blender Internal and Cycles what I can add is the following

Historically speaking Cycles is a relatively new addition to Blender. It is a completely external and standalone rendering Engine that interacts with Blender through a built in plugin and python API.
Cycles can even be used with other applications as a standalone rendering solution

Blender Internal on the other hand is integral part of Blender. It is very old, as old as Blender itself, it has been deeply improved throughout the years, but is still deeply integrated and a fundamental part of Blender, without which Blender would not work.

Its material system is also deeply tied to the OpenGL viewport preview system, that is why it's material settings and node setup are very similar to the Game Engine which uses the same OpenGL render engine.

It's also why it has a better more complete material preview system in the viewport. Where Cycles material preview is very basic and limited to image based textures without any kind of shading.

That is bound to change in the future though, Blender 2.78 already has a better preview for procedural textures, and a substantial upgrade is being made for the Blender 2.8 project.

First decoupling and removing dependencies of the Internal Render, modernizing the OpenGL real time preview, and then creating a modern substitute of Blender Internal

I know of no plugins that work with Blender rendering engines, but you can use the built in Compositor for post processing, or any external compositing software that you desire.