To summarize the reasons for going with the 3G version:
1) Resale value. I would not consider this a reason to buy the 3G version. Sure, you'll get more out of your 3G iPad when you sell it, but you're also paying $130 more up front, so it's really a wash.
2) Unlimited AT&T data plan. If you have the Unlimited data plan on the iPad 1, you will be able to transfer your plan to the new iPad. If you plan on using more than 2GB of data per month, then this would definitely be the way to go. Note, however, that you MUST keep your Unlimited data plan EVERY month - you cannot cancel at any time or you lose it. So for those who only need 3G data occasionally, this would not be worth it.
3) GPS. The 3G versions have a dedicated GPS chip, which is mainly useful for navigation. If you plan on using your iPad for navigation fairly often, then you'd definitely want the 3G. Now of course, if you tether your iPad to your iPhone, it will still have a general idea of your location from the WIFI connection, but a dedicated GPS chip is needed for pinpoint location.
4) Convenience. You pay $130 more up front for the convenience of turning 3G data on or off whenever you want. If you're not worried about keeping your unlimited iPad data plan, then you can enable 3G data at times when it's convenient for you (trips, etc). Tethering to your iPhone is certainly a viable solution, but it also drains your iPhone battery pretty quickly. So if you're just going to tether in small spurts, then it will be just fine. But I certainly wouldn't want to rely on my phone's hotspot connection for long periods of data connectivity. If you need that, then the 3G version would be a much more viable solution.
5) Cosmetic. While not a big deal to most people, the 3G version has that extra bar at the top for the 3G antenna.
Personally, I'm on a Jailbroken iPhone with MyWi and will use that as my primary iPad connection. HOWEVER, I still plan on getting the 3G iPad 2 because of the reasons I gave above. I don't mind spending the extra money up front for the added convenience when I go on trips and for the GPS chip.