Apple seems to be coming with a theme for the October 23 event. October 23 is when the iPad mini is "scheduled" to be announced, though no official confirmation has come as of yet. Reports are now surfacing that the Mac mini will also see an upgrade at the event, giving the thought that the theme is "miniaturizing."
Rumored upgrades that will be bestowed upon the Mac mini include a new Ivy Bridge processor and USB 3.0. Packing this kind of hardware into the now somewhat large (take a look at some of the stuff Intel is doing) Mac mini isn't exactly impressive, but it is nice of them to upgrade the hardware anyway.
There is a definite performance upgrade by switching out a Sandy Bridge processor for an Ivy Bridge. However, there is nothing revolutionary with stuffing it into the same package. The same thing goes for USB 3.0; nice, but not exactly revolutionary. There is also talk that there will be three versions of the Mac mini. One will likely run OS X Server and the other two will likely be a low-end and high-end configuration for consumers.