My visual imagery is also "hazy" and somehow fleeting and unreal, but still very useful. I don't find it that hard to imagine (heh) that for some people it would be more vivid, and for others almost nonexistent – though a total lack of visualization ability is perhaps more difficult to picture (heh^2), similarly to how it's almost impossible to imagine what it is like to be born blind, for example.
It would definitely be interesting if there were more discussion on other imagined sensory modalities, too. For example, as a choir singer I'd guess that, say, keeping a given starting pitch in your head is easier for people who can mentally "hear" it. Myself I can sort of imagine sounds, but keeping a pitch in my head is more about the physically preparing my larynx to produce that pitch.