From someone to whom retina definitely makes a difference:
The good news:
Text within many apps isn't as bad as I feared. Flipboard, Instapaper, Tweetbot, newspapers like the NY Times are all okay albeit missing the wonderful sharpness of the regular iPad.
Games, videos and photos (while again missing the wow factor) are likewise fine.
The bad news:
Safari is bad in portrait - basically you won't want to read it in portrait at all. Zooming is fortunately fast and fluid on iOS, unfortunately there's only so much room the screen provides even in landscape. Readable, yes. Great experience, unfortunately not. Less RAM = more tab reloads as well.
A few apps like Google+ use light text and that's not good. The App Store itself makes it painful to read the log change descriptions.
Perhaps the most painful to read are lockscreen notifications. They're small, fuzzy and look like crap. I don't suppose there's any way to resize them?
The verdict:
Even as a retina lover, the size and weight are so perfect on the Mini that overall I'd have to say it's worth the tradeoff. But it's a sad compromise and as long as I have the iPhone for comparison, there's not much way I'd ever stop noticing the lack of retina.
On the bright side, I imagine my MBA would look much better than it used to!
Hope that helps. It's up to you to decide in the end.