Altering ImageField Widget with FUpload enabled
I guess it is the line

$element['#type_name'] == 'property_gallery'


that makes your changes have/not have effect.

I would actually suggest writing a new widget alltogether, instead of altering the existing one(s). It isn't that difficult, but I don't know of any good tutorial for it online – there is a good chapter about it in the book "Drupal 7 Module Development" though, which helped me a lot.

If you find a good online tutorial, please post the link!