First off; the Mini doesn't sell well at all. Sales have been negative for some time in the USA.
Second; the Pro as it currently is will never sell well. The configuration is simply out of step with time. It is too expensive in the low end models for what you get and frankly it is just too big. Apple could give the Mac Pro a weekly rub down with essential oils and it wouldn't sell.
Third; a future machine really has no point in this discussion, they could address the Pros issues or they could screw it up even more. We really don't know what Apple is up to with the 2013 Pro. It could be a winner or another looser like the current machine.
But this isn't the case. The Mini sells well, and the Pro would if they cared about it. They're consciously not updating it, which means any appearance of a "lack of caring" is by design. Also by design is their stated promise of an update to it this year.
They don't need a screenless, mid-range desktop for any reason. That actually goes far and away against just about everything they've ever done as well as what their future looks to be.
They need a rational desktop line up not one that forces buyers to buy MBP to get a midrange like machine. That means either an XMac or a totally refactored Pro that can serve the mid range needs of a desktop user. Here is the reality the people that need a GPU supporting desktop Mac can't buy a Mini for their needs, even the 2011 model was a disgrace. The iMac for many reasons can't be used either. The Pro can obviously fill the need but the technology of the machine is generally far behind the rest of the world and it is far to expensive. It is pretty obvious that Apple either needs an XMac or a significantly refactored Pro.