If you're thinking about buying this, then you know exactly what it is. I had a 16Gb WiFi only Mini until that was stolen a few months ago. I was more annoyed about being without it than the fact it got stolen. Anyway, intended on buying another and thought I'd upgrade (and also get it insured this time!), so plumped for the 32Gb 3G option. Honestly don't know how I ever survived without 3G now. I 100% believe that it is worth the extra money, so I would suggest saving up a bit more and opting for 3G over WiFi-only. The simple convenience of being able to use it anywhere (on-the-fly gambling is my personal favourite) makes it worthwhile, and obviously once you have all your WiFi networks saved in, the 3G just bridges those gaps when you're out and about. Maps is a personal highlight.
Obviously make sure you have a good plan with your sim card - mine is 2Gb a month from Orange, £10 on top of my phone contract, and as a 'power' user, this is just about fine. Not designed for downloading films, large games etc obviously - save that for your WiFi.
Can't remember when I was more satisfied with a product that I had previously owned