the usual gui element for this kind of things is a combobox (see sections/labeles etc. in the default toolbar).
Main advantage: single click for normal export, can be changed to export all.

@sunderme look here (Edit):

(animation with 4 images)

• You can click on the button showing Export by default and the dialog asking for the target path+name opens.
• Clicking on the arrow also allows to choose Export all and the dialog asking for the target directory opens.
• The toolbutton shows the last action selected.
• Moving the toolbar to the left not only gives a better look, also buttons Browse and Import are now next to each other. This seems to be reasonable since they do basically the same (import).

Maybe interchange Browse and Import?

i have taken your code and implemented it with an apropriate toolbutton on dev