The 3G/Wifi is also used for Browsing the internet. It can come in handy when you are doing quick research, it alows you to hope on Wiki real fast and find out some back ground info. If you use the internet while your on 3G it will charge your Amazon account, if you do it while connected to Wifi it does not charge you.
There are also apps that you can read your Kindle on Computer, Phone, Kindle and many other devices.
Kindle over all for book readers, is worth it. Also i know a lot of missionaries that are going to the Kindle, because they cannot take their entire library overseas when they go, but with the Kindle they can save space and take a lot of books.
Hope this helps, God Bless.