I have reached a point where I feel confident in my good usage of the C programming language and OpenGL ES 2, except I fear I hath learnt things "the wrong way."
It is perfectly fine to start afresh, especially after serious doubts about the quality of your coding. The above quote seems like a huge contradiction to me: "confident" yet "I fear" ? President Franklin Delano Roosevelt said, "The only thing we have to fear is fear itself!"
I suggest that you should get your confidence about your coding quality before you go making game engine or support software. If indeed you have some bad coding habits, then you need to realize and correct them in the game creation stage before moving to more advanced things - as if game creation was not advanced enough for you.
Why are you in such a hurry to leap forward beyond game source coding? Only methodical learning of coding will correct and prevent bad coding habits.
I recommend that you continue only working on game source coding until your experience and confidence reach further.