Obviously there are more people learnig to use Classical Latin actively 
than learning to speak Interlingua IALA, even if the latter is much easier.

If this observation is correct any suggestion of any other auxiliary 
language than Esperanto is incorrect, as the grammar or the absence or 
presence of daft hats doesn't have any whatsoever effect on the 
propagation of an auxlang!

I can very well imagine an enormous surge of a language like Sambahsa, 
it is enough complicated to trigger those who want to boost about their 
capability of learning languages.

Perhaps the whole matter boils down to how you present the language. You 
can make Esperanto very easy and interlingua terribly complicated, 
depending how you present them.

Kjell R