Israel should take the Sinai, the West Bank, the Golan, and Gaza
They already hold the Golan Heights and West Bank. They gave back Gaza because it offered them nothing and caused problems, though now they may be rethinking that. In their perfect world, they can go in, crush their opponents and come back out. No one in Israel wants to occupy it for any length of time if they can avoid it.
I have no clue why Israel would even think about taking the Sinai. Goodbye peace treaty with Egypt, hello to a lot of land they have to occupy that gives them no benefit. Hello even more world condemnation and a pissed off Arab world.
If I had to bet, the reason Hamas started firing the rockets now is because the rest of the Arab World doesn't care about them so much and is much more interested in the Arab Spring and in many countries there internal struggles. Taking the sinai (or even Gaza) would put everyone's attention squarely back on Israel.