I faced the same question when I bought my Kindle last year and after much to and fro decided for the 3G version because it felt more luxurious and I talked myself into it reasoning I could use the 3G feature more when traveling abroad (it's not of much use here in Germany outside of buying books). Since then, I have used the 3G feature exactly ONCE: I was in public transport, had just finished one book and decided to get the next in the series. Without 3G, I would have been like 10 minutes without THIS book (I could have read any other though)...
And yes, I think this was an impulse buy - if I remember correctly my thought process was like this: "Oh, hm, this is the last page in this book. Should I get the next one in the series? Hey, I have never used this 3G feature I paid so much for... let's buy the next book while sitting in the train, that'd be cool!".
As you can see I don't think the price premium is worth it. At all. When pre-ordering the newest Kindle a couple of days ago, I didn't even need to think about it.
Yes, it is nice to have. But - for me - it wasn't worth the price (almost 50% more!).
Since you say that you are rarely out of WiFi coverage and don't travel much, I don't think it would inconvenience you much if you saved the money (how many books could you buy with 60$
) and got the Wi-fi only one.