I would eBay my iPad 3 and upgrade. I like my 3 a lot, but a lighter weight would be much nicer, plus I've been wanting a faster processor since I'm a heavy multitasker and use some of the more sophisticated productivity apps and work with large, complex documents. I would benefit from more speed. But I held off on the iPad 4 because I just bought the 3 last spring and I know a better form factor is coming.
I'm not sure what to think about the likelihood of a March release. It seemed like it was going to happen, but then iLounge and other reliable rumor sources said fall was more likely, then Apple released a 128 GB iPad 4, but yet we are still getting an awful lot of iPad 5 rumors already including components. This pickup in leaks usually happens a couple months or less before a new product release.
So who the hell knows. Maybe we're looking at June.