The only reason, that I can see, to wait for the iPad 3, is for the retina display and better cameras.
As most people have already said: there is no chance of retina display in the iPad 2.
But, I think there's 50% chance of the iPad 3 having a retina display. When thinking of the retina display you have to include these factors:
Can the GPU push this many pixels: the Tegra 3, being released fall 2011, can push 1920x1200. If you think at the end of 2010 you could push 1680x1050 (Tegra 2), and after a year you can push an extra 240x150, it could be possible to have a GPU that can push 2048x1536 (extra 128x336) ready by April or WWDC. But I think it'll take more time to create a GPU, that can push an extra 128x338, baring in mind that it will take a year to increase the res that a mobile GPU can push, by 240x150. iPad 4 is more realistic and the Tegra 4 will presumably be able to push 2***x15**.
Also, how much will it cost to create a 10inch display with a resolution of 2048x1536?
Heat generated by GPU?
Dead Pixels?
Speed of device when playing games?
Can the company that makes the displays keep up with the demands?