Yeah, I realise this. I was in a rush to write that last post, I did not have much time.
I still think it would be useful, maybe a warning would be needed. Or perhaps calculating the minimum amount of memory would be needed (Texture area * 32) as you already calculate the attachment area. It still wouldn't be accurate but at least the artist(/who ever) has a way of seeing how much memory they are using.
Obviously you can not run the texture packer all the time when spine is running, but you could just calculate it anytime a new attachment is added. This too, could lead to performance problems when using spine. (using the script) so maybe a button to calculate it, or a tickbox (off by default) to automatically calculate the amount of memory the textures are using, anytime an attachment is changed.