technically you're right, its not inverted cuz you spin horizonally around your body, but its so close to being inverted that yes, depending on the person, it could deff help with inverts like rodeos and others, and just that feeling and not freaking out in the air.
but tricks you should deff have down before modifying any spin, would obviously the basic spin itself. i wouldnt say you need to be able to 9 or 7 to be able to flat. i also wouldnt say you need to be able to do a 180 before a backflip. if you can stomp the basic spin most of the time, then you are prolly ready to modify it going inverted or whatever you're trying. however, some people find certain rotations easier, and might land diff tricks at diff times, so its kinda personal preference.
but no matter what, when trying a new trick, make sure you feel comfortable and are safe doing so. when its rained for 3 days and you cant even ski down the trail cuz you have no edge, dont go trying new stuff. if you dont have the basic spin down, chances are you might not get the rotation, but you most likely wont land it. some are luckier than others, but i personally try not to push my luck too much and know what im trying.