Economic development in Gaza depends less on the miraculous discovery of natural resources and extractive industry than on politics and social history.
Until the Palestinians in Gaza stop thinking of it as a temporary way station or refugee camp while they wait for some Deus Ex Machina to wipe every Jew off the planet so they can reclaim their great aunt's bachelor flat in Haifa, which no Arab has set foot in since 1948, and actually start building a functioning, modern state in situ, they will not advance economically.
If they put half as much effort into higher education (leading to 21st century industries like finance, software development, electronics manufacture, shipping, tourism and media) as they put into rocket attacks, blowing up pizza parlours and assassinating fellow Arab politicians and journalists, they would be much better off economically.
Take tourism as an example. If you were looking for a place to spend a week long holiday on a Mediterranean beach, with occasional sidetrips into historic ruins and local cuisine, would you pick a war torn, factionalised refugee camp or would you just have it over with and go to Corfu or Ibiza again? If you were an investor in Dubai looking to situate, say, a printing plant for Arab language dime novels would you put it in a terrorist ridden, politically unstable war zone, or just get the things printed in China like everyone else?
The number one, and only truly indispensible ingredient for economic development, is a stable and relatively peaceful society. Until that happens, nothing else can.