I know it's nice to have, but I've had an iphone 4 since it came out and have NEVER used that feature...my son has one as well...we have a macbook w/ a camera and Lion...never used the feature...so I doubt adding an ipad will inspire me to use facetime
well...we have four in our house...even the youngest has a frequent need for a computer, and sometimes to play minecraft...whatever the case, we fight over access to this mini (as it was the only one that wasn't too slow). We have an older G4 mini and a similarly spec'd G4 iBook...but neither of these has us fighting to use them...we added a late '08 unibody macbook which is similar to this mini...so that's an improvement, but ultimately I expect to use it mainly for browsing, email and some apps. Three out of 4 of us have iPhones, so it's mainly as an outlet when everything is backed up.
It's $330 less than a comparable iPad 2...That's the real temptation. I have a kindle for books, so, while I'm sure I'd use it to read books, the kindle is still better for that task.
If you think you'll need the 3G, get the 3G. If you think you can live without it, get the iPad 2. The form factor and increased speed is worth it for the iPad 2 IMO.
I wouldn't look at it as just speed but as long term use if that matters to you. What you would or wouldn't miss really depends on you. It doesn't sound like your usage is that heavy but at some point support for the original iPad will be dropped before it is for the iPad 2.
Does the additional 16GB matter to you? Does 3G (and GPS) matter to you? These are questions you need to ask yourself to evaluate the options.