Hi Jam,
A few thoughts...
Apart from those things already mentioned, I think that there are two reasons why larger layouts of the roundy-roundy variety tend to attract more time and attention from viewers. Firstly, with the larger size tends to come the feeling of space and the railway being set into the environment whether urban or rural . Secondly comes full-size and regular train movements.
I think you and others have shown that it is possible to achieve the feeling of space equally well in a small layout. With your effective use of a photographic background and the slightly unusual shape making use of the features of the prototype, particularly at the beach, I think you can make your layout seem much larger and thereby potentially more interesting to viewers.
The second, I suppose, is slightly harder. Although trains on a prototype like Calshot would be smaller than say a mainline station, you don't have the space for very long trains nor would a very frequent service be likely. I think if you can find an interesting balance between standard gauge and narrow gauge, passenger and goods and give viewers enough to watch whilst maintaining realism and not overdoing it (which, as with detail, many layouts fail to limit themselves in effectively) you will have a successful small exhibition layout.
I have also always found it easier to chat to an operator about his/her layout if it is fairly small and there is only one operator. Of course this is not always so and depends on how proactive and responsive the operator is. I think that, regardless of your age, if a viewer can see you have some skill from looking at your layout and then gets a sense of your interest and enthusiasm on speaking to you then you will be a success.
Finally, I don't think you need to be so modest when it comes to point 4) on your list. Your modelling is already quite impressive and constantly improving (as hopefully is everyone's!). I can't wait to see how this is going to progress.
Sorry for rambling. Hope some of my thoughts are helpful - I'm still racking my brains for some more practical ideas I can suggest for the layout and how you can fit in all the features you want but I doubt I'll come up with anything better than you will anyway!
Peter