I believe that the K-7 can attract back users who "jumped ship" from Pentax to other brands. At least it shows that Pentax is still a player in the game. The K-7 is an important product because it shows that Pentax is alive and kickin', despite all rumours about Pentax is dead or will be dead, or will be closed down by Hoya or will be bought up by Samsung or all those stories that has been floating around since the Hoya take-over.
If the K-7 isn't a sign of comitment from Hoya, then what is?
The K-7 may not get so many users from other brands, those with a large collection of Nikon or Canon lenses are more surely to upgrade to a new Nikon or Canon than a Pentax, but the K-7 can make Pentax as a brand more interresting to invest in for those who wants to upgrade from a p&s compact.
Oh, and the K-7 also shows that the argument from 4/3-field about 4/3 being needed for a compact DSLR system, is no longer valid.