In my opinion, stars earned by taking and holding Tokyo should scale with the number of players. Otherwise, the strategy is to stay the heck out of Tokyo, buy cards, and then roll for your stars once you acquire enough power-advantages.

With 4 players, you have to weather 3 rounds of potential attacks to get the 2 stars for endurance, whereas in a 2 player game, you only need to survive one round of potential attacks to get the bonus. Furthermore, as you are yielding more often in order to not-die, other players are getting a star for it, so the advantage is less.

The expansion balances this a little better because of powerups. Though I think it more depends on who you play with.