If, as many are suggesting, Apple upgrades the mini to specs similar to the new low-end MacBook (which I doubt) the price would probably increase to $899 or $999.
This one sentence moves me to write the reply and I think you are wrong. Of course I don't have any internal information, but #1 selling Mac desktop on Amazon, you can hardly buy it on Refurb Store, because they just sell very quick and the price on eBay gives another view at the so "bad selling" MacMini.
That might very well be a valid reason. We hear constant complaining on this board that Macintosh computers are too expensive for what you get, so it may very well be that there are a lot of people who want OS X, but cannot afford the $1000-2000 that most Macs command so they buy the Mac Mini.
Such a trend would mean that all those who claim the Mac Mini has poor stats are not wrong, but that the significant majority of the market for the product doesn't care about stats. They want OS X and feel even a Mini with a 65nm CPU and an ancient IGPU is "good enough" for it so Apple has no reason to make it better because if they did, it would get more expensive.
That 13" panel likely costs Apple less then $100 to source, so a Mac Mini with identical components to a MacBook could easily run $799 or even $899. The market really prefers portables now, even if they never run off the battery, so if the price difference is $100-150, chances are the majority would buy the MacBook, instead. I notice the Mini dropped to #8 on the list preceded by the new and old MacBooks, MacBook Pros and even Applecare. However, this could be expected since new product drives new sales.
It is unfortunate that Apple no longer breaks out sales by model, but in Q1 2008 of the 2.4 million units they sold, 1.4 million were notebooks. So that means they sold 1 million Mac Pros, iMacs and Mac Minis. That's not a bad haul, and even if the Mac Mini was just 10-20%, that is 100,000 to 200,000 units.
However, if it is a low price that is driving Mini sales, then those who believe that the Mini will see a huge stat bump are likely going to be very disappointed. We could see, at best, the most mild of stat bumps. Perhaps an nVidia 9100M or 9200M instead of the 9400M. Maybe only one CPU option - the 2.1GHz T8100. And maybe only a 200GB or 250GB HDD. The goal would be to keep it cheap while still making a nice margin.