To be honest if you play the "waiting" game you will wait forever. Apple change the iPhone and iPad on a yearly basis (or thereabouts) so if you wait for the rumoured iPad 3 (which i dont think we will see till Xmas at the very earliest) you may as well wait another 12months for the iPad 4, then for the iPad 5 etc etc.
I went from a 3G iPhone to the 3GS then to the 4. (the difference between the 3GS & 4 is massive Tony). Each time i do so (because of my contract) it cost's me nothing to change and i was actually £37 better off last time i changed.
I got the iPad on launch however haven't upgraded to the iPad 2 as the one i have now does everything i want it to (and the wife said i can have an iPad or a new car. iPad lost
). The only time i will consider a change of iPad is when they increase the memory.
I really don't see the point of having a load of extra add ons for the iPad either. If you want to be able to use it like a computer/laptop then buy one of those. If you want a portable entertainment device which also enables you to do productivity on the move, read books, browse the internet, play games, watch videos or listen to music then buy an iPad.
As soon as you buy the latest device it is already 6 months out of date anyway. The final decision on the production model of that device was made 6 months earlier and it was put into production then launched. In the mean time said manufacturer is already 6 months into developing the successor so you are always going to be behind the curve.