It is still there, exactly as described in the Wiki, here:
http://wiki.jriver.com/index.php/VisualizationsSee also:
http://wiki.jriver.com/index.php/Visualization_Studio (I've updated the description on this, and added some images, to correct it.)
Wait. Actually, it isn't under Playing Now any more by the look. It is accessed via right clicking on a Display view while playing something, in the same way that actual visualizations are selected.
The attached image shows where I have popped up the menu that shows where it is on a Detached Display. The Playing Now Display Pane is also a suitable Display view to right click on, as per the Wiki.
But I'm not sure it is actually what you want, given what you want to do. But I don't use visualizations, so I don't know what can be done with the studio.
Note1: On a couple of visualizations the Visualization Studio menu item didn't seem to display. I didn't take note of which, I just changed visualization and found it.
Note2: I managed to crash MC several times when changing visualizations while music was playing, so watch out for that.