Hi Martin, what type of hot-spot are you using that shows the different sharpness (ie, image, html or plain text)? If you test my link above, it should show the same sharpness for all three types of hot-spots that you see in that sample in IE, Chrome, FF, Opera, etc. That's what I see here.
If you are using the HTML hot-spots (where spot's presentation is defined via html script that you can enter in SpotEditor), the sharpness of the images inside can be slightly different if you scale the image inside the wrapping element of your hot-spot html script, which would boil down to the varying resizing algorithm in browsers that I pointed out above. But then again, send us your 360 view sample and we will investigate and confirm
Your inertia example looks good as long as you are modifying xml directly (in the absence of SpotEditor support, which is coming very soon!)