I disagree with Steve. I think that the 520 is enough of an improvement over the 510 that it is worth waiting for the price of the 520 to come down. I am in the same boat myself. I'm hoping that the prices will have dropped by the middle of October. Maybe I'm being an optimist here, but I do not think we'll have to wait till after Christmas.
Note that the 520 will come in various kits. All have the 14-42mm, of course. There are two versions of the 2-lens kits, one with the 40-150, the other with the 70-300; there is even a 3-lens kit, including all 3 of these lenses. I think I'd go for the 3-lens kit, which is only $100 more than the 2-lens kit that has the 70-300, so you are essentially paying $100 for the 40-150.