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Cnet has a good comparison of the Surface Pro 2 and 3, complete with a comparison chart. You might find it of interest. http://www.cnet.com/news/whats-new-with-the-microsoft-surface-pro-comparing-surface-pro-2-specs-vs-new-the-surface-pro-3/
The keyboard's trackpad and the built-in "kickstand" are improved to make the Surface Pro 3 feel more like a laptop when you are using it with the keyboard. In fact, that is one of Microsoft's selling points about the tablet - that it is more like a laptop than other tablets. Whether that is a good thing or not depends on what you are looking for in a tablet, I suppose, and you could get a pretty decent laptop for the price of a Surface Pro 3. The screen is also larger, while at the same time overall thickness has been decreased. There have been other evolutionary hardware improvments, but nothing too significant that I can think of off the top of my head. Whether it is worth it or not is a personal decision, but considering that this is a premium priced tablet, I would probably not be willing to spend the money to upgrade if I had a Surface Pro 2. That's just my opinion, though.