I yearn to do great works of engineering and art, which I consider what you have done.
How do you come up with ideas?
There's coming up with a good idea: learn how to not get buried in your ideas (most are mediocre down to bad even for people who have "good idea skills"!)
I write down ideas in notebooks to get rid of them. Every once in a while one will capture a different point of view.
And, there's the Princeton Tea joke of scientists comparing what they did for ideas. One says "I have them in the middle of the night so I have a pad by my bed". Another says "I have them in the shower so I have a grease pencil to write them on the walls". Einstein was listening and they asked him about his ideas. He said "I don't know, I've only had two!"
(Some people are better at filtering than others ...)
What he said was important was to have a big horizon, at least 10 years. Anything less would not do.
Then envision what should be possible in that time. "It would be ridiculous if $X wasn't possible in $Y years" and then backtrack on what would technically be required to make that happen.
Rinse repeat. He said that with good company support and a good team, you often found yourself delivering at half that time none the less (but again, you should never constrain yourself to that little, or else you will stress towards performing, instead of thinking properly about the problems needing to be solved).
Alan: Hope I didn't butcher your message too much :)
[1] I think it might be this one, but I honestly haven't checked. See it anyway. It's a good talk. https://www.youtube.com/watch?v=NdSD07U5uBs
So I'm guessing that there is a path for you to imagine images. It could be very similar to how most people who think they are tone deaf can be helped to hear pitches quite accurately.
Most of my ideas come in "waking dreams" (this is a state that most children indulge in readily, but it can be retained in a more or less useful way -- I don't think you quite get into adulthood by retaining it, so it's a tradeoff).
Main thing about ideas is that, however they come, most of them are mediocre down to bad -- so steps have to be taken to deal with this major problem.