I'm attaching a 2017 file with an example symbol. The main reason I am going through this trouble is that I find the event seating tool clunky and annoying. It is much faster for me to manually drop symbols in that have spacing locus and duplicate as necessary. The main reasoning behind dropping table arrangements in as groups is that I can count individual symbol instances in the file, for quick and easy chair and table counts, as each chair and table is a unique instance of it's symbol inside the group. There are probably better ways to do this with scripting but at the moment this works for me.
My big issue with the event seating tool is that it gets annoying to use when table placement is not perfectly aligned. Often I am dealing with tight banquet rooms and making sure things will fit means nudging things around, which can not be done with seating blocks, the spacing is even throughout the block. Then dealing with multiple seating blocks means it's faster to just drop symbols and nudge as I need to. The tool is great for things like large chair layouts, where spacing is much easier to assume will be even and won't need to be nudged individually.
Aside from this particular purpose though it still baffles me why I can not have 2d information stored in a blue symbol that can get inserted in to the plan view on the layer plane. I use blue symbols a lot for PIO and other geometry stored together, like a screen PIO sitting on a truss frame that is built with truss symbols and other non-symboled geometry. Geometry that is otherwise not a symbol itself will not insert to the "opposite" view, 3d won't insert when working in plan, and plan won't insert when working in 3d. Really my basic question is why any and all 2d and 3d geometry inside a blue symbol just does not get inserted to the appropriate places at all times. As I stated originally my only assumption is that it's working on the same principle as the 'convert to group' command.
@Kevin, maybe I am missing something but I am not seeing how you can have geometry inside a blue symbol assigned to the layer plane, my only options are screen and symbol definition, and symbol definition geometry, being stored in the 3d portion of the symbol, will not insert to the group when working in plan view.
test.vwx