Probably not; but the real questions are:
1) Would it sell enough to be a viable product? The hard core gamers are not really part of Apple's market; nor a big enough slice to warrant producing a machine aimed at them.
2) What would it cannibalize? Would it replace Mac Mini sales? Or would graphic professionals find it powerful enough to replace the Pros? I doubt it would replace a MacBook; but it probably would impact other Macs sales.
In the end, while a mid tower would be nice, I don't see it creating it's own space and expanding sales as much as cannibalizing others; plus given Apple's history of keeping Macs as standard as possible I doubt they'd create a low end configurable model.
I'm not sure iI agree with your iMac assessment - when we bought Macs to replace our aging Mac production equipment for a newspaper we went with PowerMacs because they were cheaper than the equivalent Apple products. I don't doubt other orgs made the same choice.
That's almost word for word what people said about the Apple Store chains in 2000 and the iPhone in 2007 (too expensive, lacks 3G, no market for it).
Until it's tested, there's no way to determine yes or no, but I do know that there are a lot of people in need of this and there wasn't much clamoring in 2006 before the iPhone came out in 2007.