I guess it doesn't suit everyone, plus I presume you are using the JVC for scaling: I use an external Lumagen VP for the vertical stretch which I think gives a better result (more obvious with test patterns but still there non the less).
However you are also at a shorter throw than me. What this means is that with a lens in place I am able to use minimum zoom in the projector, so I get maximum contrast. If I zoom there is quite a change in the light output (such that the brightness is almost the same zooming verses lens), but equally there is a bigger change in the contrast over this range too. At your shorter throw you possibly won't get the same change of contrast and light output that I get since you are more in the mid range of the projector's zoom.
When I compare zoomed to lens 2.35:1 I get a sharper, higher contrast image that looks less 'coarse' than zooming, but it's a combination of my very long throw and the Lumagen VP. I also have a TV partly showing below my screen and the screen wall is flat dark brown paint, so the lack of black bars is more noticeable in my room.
Horses for courses as they say: At least you've tried it and there is a ready market to sell it on (this was why I took the gamble to buy my Isco II, but I've kept mine).
Just one final thing though: Have you adjusted the Isco's focus correctly and evened out the pincushion? Since you say the image is sharp and don't mention pincushion I'm guessing you have, but if not put up a white grid pattern (after focusing the X30 without the lens in place first) and adjust the Isco focus so that the grid is as sharp as you can get it.
"Don't believe everything you read on the internet". William Shakespeare 1615