Since the mines opened for me (is that just a level thing, or are the mines a new feature just added?) I've mined with enough dynamite to expand my new little island three times. I am likely not the worlds greatest player and I have plenty of neighbors who are far more advanced than me level-wise, but I was visiting a few islands today, and all of their dynamite based islands are still just that one little block waiting to be expanded...
Are expansions of that island just not showing when your neighbors visit, or am I the only one who's dynamite (and bomb -- I'm only two a way from crafting my little whatever it is dragon) crazy?? It is SUCH a good way to supplement your apple stock, I praise the almighty for it!