Wait until the iPad 3 comes out. I will be replacing my original iPad as soon as it does.
Why? Just curious, I have the original iPad - I was one of the first pre-order customers when the origional was available for pre-ordering. Got the Wi-Fi only 64 Gig, and I use it daily.
Primarily, I use it for emailing, web surfing and reading. Love the Kindle App, and finding myself actually preferring it to iBooks in that I can retreive my Kindle books on any device; instead of being locked into Apple devices.
I have some DVD ripping software (Cucusoft) and rip my DVD collection down to ~1 GB files, so I have ~30 movies with me at any time. But, here's why I am wondering why you want to upgrade - as I can't see any compelling reason. Retina display means I need to increase my movie filesize to realize the improved display. Game play on the iPad is marginal - as you are placing your fingers all over the screen, it's hard to be immersed in the game (unlike a console). I can wait 3 seconds for my books to load, I just don't read that fast. 10 hours battery life after 2 years and I'm fine with that. I Hotspot to my iPhone, so I cannot see a reason to get the 3G/4G accessory. I do like the iDVD softare, which does not run on the first generation - but that is the only reason I can see in upgrading. All in all, the orgional iPad was a 9.95/10 product, with the iPad 2 being 10/10. So, why do you want to upgrade? Just curious ... I'd love to get a 'new' one; I just can't justify it.