For me, the bottom line is: If you get the 3g, you'll find ways to use it.
I use it all the time when I'm driving out somewhere and don't have wifi handy. It was convenient when I crossed into Canada!
On the flip side, if you get Kindle WiFi, you won't miss 3g.
This is because when I don't have the internet, I just shrug and keep reading. For traveling... do you remember when you put all your songs on a tape/cd/mp3 player right before the trip? The same will happen for the kindle. You'll put all the books you want to read before a trip and so you really didn't need the internet to get new ones. As for browsing, it was said before that the 3g speed isn't crazyfast, but it's manageable.
So in conclusion I think: You won't miss what you never had. But if you get the 3g, you'll love it (psychological rationalization of your premium purchase). You'll be happy with whichever you get
