Imagery doesn't seem to produce after-effects like vision does. For example, staring at red bars and then looking at a white background will cause you to perceive faint green bars. Imagery also doesn't seem to lead to repetition priming effects. For example, imagining words in lower case doesn't seem to improve perception of those words. This is a relatively new area of research, so maybe something will emerge here.
Vision supports both.
But, if you're interested in cognitive, here's a big area where there's plenty of work to be done. You can get a look at a person's brain as they form a mental image vs. do a verbal task. It's sort of a mix between cognitive approaches and neurological approaches. Another possible resolution may come from additional interference experiments. Basically, if you tie up the parts of the perceptual system that perceive a particular kind of stimulus, that should hurt imagery as well.