From some light introspection, it seems like my mental imagery is comparable to yours, but probably somewhat better. (E.g. I would mostly answer 4s to Marks' Vividness of Visual Imagery Questionnaire, with a few 3s and maybe one or two 2s in there, however all images I see are very fleeting/morph rapidly.)
So, with that said, the "full" (as opposed to momentary, fleeting) visualisation I find easiest while (mostly) awake is that of locations I'm familiar with. I can imagine myself in a room in my house (or previous houses I've lived in), and "look" around, taking notice of objects that should be in various locations. By mentally examining each area in a room in detail, I can bring to mind what should be where and add it to the "image". Eventually, I'll have built up a decent moderately visual image of the room (if I'm fully awake, it's not completely vivid, but I can move as I please and be able to tell what sort of vague picture I should see when looking in any particular direction). You could perhaps try doing that sort of thing and see if it helps and maybe it'll help in more general cases too (possibly).
The other thing you could try is self-hypnosis. There are a lot of files floating around the internet that allege to help you visualise some scene, and some of them purport to be things like "imagination training" and whatnot. Mind you, from my brief attempts, they completely failed to work for me (in the sense that I failed to get hypnotised), but since you have experience with meditation, maybe you'll have an easier time with it. Admittedly, I suspect this won't help, but if you're running low on ideas, it might be something to try.
Previously: Generalizing From One Example
Summary: I do not have visual mental imagery. I want it. How do I get it? What exercises, if any, will help?
In further detail... Here's Francis Galton's Statistics of Mental Imagery paper. I'm not quite at the 3% level of completely unable to form mental images, but I'm close. In particular there are three times I have vivid, sharp mental imagery, and the existence of such times tells me I have the brain hardware to visualize. It's enough to let me know that I want it all the time. Unfortunately I don't know how to get it. And searching online has proven difficult and frustrating... for example this article is first of all about a different meaning of "visualize", it's talking about some kind of self-help motivational thingy, and second of all it starts by saying "How to Visualize: I want you to relax and close your eyes. Picture a hot, sunny day at the beach."
Full Stop. Halt, Catch Fire and Burn.
That's already too far. For those of us who don't visualize, practice definitely does not consist of pulling up mental images, playing with them in new ways, and expanding our imagination. I'm very good at imagination in some ways, but I lack that first ability to pull up a mental image. That's what I want to learn how to have!
Here is a description of what I can do, what I have tried, what I have learned, etc.
I see vivid visual mental imagery in 3 situations: