I had the same thing to consider when I bought my iPad2 wifi only.
3 weeks later, it works great and for me gets along nicely.
For me, I most miss the assisted GPS feature. This is nice when locating stores/restraunts.
In my opinion. IF I had an extra £100 and could afford another data bill, I would go for the 3G version.
But for me the positives of saving money outweigh the inconveniences.