A dedicated invert show focussing on T's is a great idea. It should be on a Saturday, one day only, with talks, a show, and an auction in the afternoon followed by a braai. The bar can be opened at the start of the auction - it makes bidding better and less painful. The auction must be of nice to have T's and the entries advertised well in advance.
I think a show that displays a wide range of species, as well as sections for best prepared habitat, biggest T, etc would be a good idea, with sponsored prizes.
I am looking forward to this event, and will start saving my money!