Not worth the wait
I would just buy the thing right now. Three reasons:
1) Who wants to wait an indefinite amount of time? You're on Steve Jobs's schedule, which means you'll probably have to wait months for the thing just to get announced, then another few weeks/months for it to go on sale. Too much waiting. Play that game, and you'll always be waiting for the next big thing.
2) There aren't going to be any major improvements, as far as I know. Cameras probably, but as you say you have an iPhone 4, there's no real point. The camera on that is great and just as portable, and you can already Facetime on it if you want to. Personally, I don't videochat much, if at all, myself. A bigger memory option, perhaps (for more money) and probably a speed boost. There is some clamoring that there may be a USB port on the iPad 2, but I don't see a terribly large benefit in that. Even if you could plug things in, there would be virtually no peripherals that would work with it. Has everyone forgotten that you can buy the Camera Connection Kit? That takes care of your camera needs. Nothing else would really work with the iPad. If anyone has any ideas, I would love to hear them, but I can't think of any. Perhaps if there were to be some major, groundbreaking update such as a new form factor (too soon) or a retina display (technologically not possible right now), which aren't going to happen, despite what some people say. These people are deluding themselves, or don't know what they're talking about.
3) It's an iPad. Who wants to wait? With the new iOS 4.2, it's going to be even better than it was when you had your last one. Multitasking adds a whole new element to iPad. If it does everything you want/need it too, there's no real reason to wait.
BTW - does anyone else have trouble with this? I flip my magic mouse around absentmindedly while I'm typing, and when I go to grab it again, it's facing the wrong way, so my mouse goes in the wrong direction. I feel like an idiot.